By what age must one be married:
In any event, one may not pass 20 years of age without being married [and is thus to place effort to be married prior to reaching 20 years of age]. One who does not get married by 20 years old transgresses and nullifies a Biblical Positive command. [If, however, he is not married by twenty years old due to matters beyond his control, then he does not transgress any prohibition. Likewise, some Poskim rule it is permitted to delay marriage until 24 years of age in order to find a proper Zivug, or due to other reasons.] One who passes 20 years of age of and does not wish to get married, then [in previous times] the Beis Din would coerce him to marry in order to fulfill the Mitzvah of having children. However, in today’s times, one is no longer coerced by Beis Din to get married.
Delaying marriage past 20 due to learning Torah:
If one is involved in Torah learning, and toils in it, and fears marrying a woman lest he be required to toil after sustenance and thus nullify his Torah learning, then it is permitted for him to delay getting married [even past the age of 20]. [Some Poskim rule he may delay marriage for as long as he wants, so long as getting married will prevent him from learning Torah due to the need for him to get a job to support his family. He may likewise choose to marry a woman who is infertile in order so he can dedicate his entire life for Torah learning. Other Poskim however rule there is a limit to this matter, and one cannot delay marriage forever. Some Poskim rule that one may delay until 24 years of age. However, according to Admur, he may delay marriage until he learns and remembers the entire oral Torah in a summarized fashion, if he is capable of doing so. Practically, in many Litvishe Yeshivos, the custom was to delay marriage until the early 30’s. However, the practice in Yeshivas Tomchei Temimim was, and is, to get married in the early 20’s, and so is the proper approach. Chabad Rabbanim and Mashpi’im around the world have proclaimed the necessity for Bochurim to begin Shiduchim as soon as they complete their study in Yeshiva Gedola. At age 20, they are to begin their search for a wife, and only those who are truly dedicated to assiduous Torah study may delay for another one to two years. A similar ruling has been given by other Gedolei Yisrael of today’s generation.]
Delaying marriage forever for the sake of learning: Furthermore, one whose soul yearns to learn Torah constantly like Ben Azaiy, and he attached himself to it his entire life, and thus did not get married, he carries no sin for doing so. [Some Poskim rule this applies even if getting married would not trouble him from his learning, such as he is wealthy. However, Admur negates this opinion, and implies if one is able to do both, to constantly fulfill his Mitzvah of Yedias Hatorah and get married, then he must do so. Some Poskim rule that initially, even one who desires to learn like Ben Azaiy, must get married, and it is only after the fact, if he did not marry, that he carries no sin. Furthermore, some Poskim rule that a person of the such stature and nature of Ben Azaiy is not found at all today. However, from Admur, it is implied even initially one may choose to follow Ben Azaiy and not get married in order so he can constantly review his Torah learning and not come to forget parts of the Oral Torah and his Mitzvah of Yedias Hatorah. Nonetheless, even in his opinion, the Sages advised one to get married once he has completed his Mitzvah of Yedias Hatorah, even if there is worry that he may come to forget. If, however, there is no worry of forgetting the Mitzvah of Yedias Hatorah, and he simply wants to delay marriage in order to continuing learning the depth and Pilpul, then it is forbidden to do so, even according to Ben Azaiy.]
Who may delay marriage past 20 for the sake of Torah learning? One may only delay marriage past the age of 20 due to Torah learning, on condition that his inclination does not overcome him with erotic thoughts to the point that his mind is unable to focus [and he is able to thus learn without thoughts of sin]. If, however, he is troubled by erotic thoughts to the point that his mind is unable to focus, then he is to first get married, in order to learn Torah with purity of mind, without erotic thoughts. [The Rebbe encouraged this approach.] Furthermore, this allowance of delaying marriage due to Torah study is only for a person who has the intellectual capacity to learn and remember the entire Oral Torah, in which case he is to first learn the entire oral Torah and only then get married. This includes all of the laws; all the 613 commands together with all their details, Biblical and Rabbinical, and their summarized reasons. If, however, he does not have the intellectual capability to learn and remember all of the Torah, then he must get married prior to the age of 20.
One is to get married at 17/18 years of age, and no later than 20 years of age. It is permitted to delay marriage due to Torah learning, if certain criteria is fulfilled, as explained next. Some Poskim rule it is permitted to delay marriage until 24 years old in order to find a proper Zivug, learn Torah, or due to other important reasons. The Rebbe strongly advocated for bringing down the marriage age, and encouraged people to get married starting from age 18. Nonetheless, the Chabad custom in Yeshivos is for Bochurim to get married in the early 20’s. Chabad Rabbanim world over have ruled that at age 20, Bochurim are to begin their search for a wife, and only those who are truly dedicated to assiduous Torah study may delay for another one to two years.
The criteria for delaying marriage due to Talmud Torah:
According to the ruling of the Alter Rebbe, the allowance of delaying marriage past age 20 for the sake of Torah study only applies if the following four conditions are fulfilled:
1. One is learning Torah and is capable of fulfilling the Mitzvah of Yedias Hatorah, through learning and memorizing all the details and reasons of the 613 commands, in a summarized fashion.
2. One will be unable to fulfill this Mitzvah of Yedias Hatorah if he gets married, due to his preoccupation in making a living to support his family.
3. One has not yet already fulfilled the Mitzvah of Yedias Hatorah. If he has already fulfilled this Mitzvah, he may no longer delay marriage, unless he is worried it may lead him to forget his Torah learning.
4. One is not troubled by erotic thoughts that prevent him from learning Torah in purity.
Practically, by what age must Yeshiva Bochurim today get married by?
As stated above, in the summary, the Rebbe strongly encouraged people to marry early, from age 18, although the current custom mentioned by the Rebbe, is to marry in the early 20’s. The Chabad Rabbanim in recent years ruled that at age 20, Bochurim are to begin their search for a wife, and only those who are truly dedicated to assiduous Torah study may delay for another one to two years. We will now explore whether this custom of delaying marriage past age 20 has Halachic basis.
Is there a Halachic allowance for Yeshiva Bochurim to delay marriage past age 20 for Bochurim today? Based on the criteria mentioned above, from the letter of the law, in today’s times, most Yeshiva students do not have a Torah learning allowance to differ marriage, and must get married before the age of 20, as most students are not born with the intellectual ability to learn and remember the entire Torah. Furthermore, even of those who are able to reach this state of learning, many are troubled by erotic thoughts. On what then does the custom rely upon to delay marriage past age 20 despite their ineligibility for the allowance of the Torah learning deferral? This will be addressed next.
On what do people rely upon today to delay marriage past age 20, even if they do not fall under the criteria which allows delaying marriage due to Torah learning?
Seemingly, Bochrim today are not mature enough for marriage until their early 20’s, and hence, irrelevant of the Heter of learning Torah, they are unable to marry beforehand. We find basis for this approach in the Poskim who state that the dictum of the Sages which encouraged marriage from age 13 is no longer applicable today due to the change of times, and lack of maturity. Hence, seemingly, the same would apply regarding even past age 20, that if times change, and people are no longer mature enough to marry this early, then the marriage age automatically becomes delayed. In other words, the Torah did not obligate one to get married by any specific age, and rather obligated one to get married as soon as is able to, once he becomes Bar Mitzvah. Now, in previous times, since Talmudic Torah learning extended from age 15-20, therefore the marriage age was up until age 20, to suffice one to learn five years of Talmud. We see from here that delaying marriage for a necessary purpose is permitted. The same should certainly apply to delaying marriage due to lack of maturity, as if one is not mature enough to marry, the marriage will not last, and certainly the Mitzvah is not yet applicable to him. Alternatively, one can say that the age by which one must marry is dependent on the community system, and if the system in one’s community is to only marry after age 20, after concluding the educational system, then for that community, the marriage age is differed until later. This is similar to the establishment of the original age 20 which was based on the system to learn Talmud from age 15-20. Vetzaruch Iyun on all the above, as no matter what one says, it contradicts the simple ruling in Shulchan Aruch that one must marry by age 20 without giving any exception to the rule, unless one is learning Torah. The above is thus only a Limud Zechus on the current custom, in order to defend how it does not transgress the clear ruling in Shulchan Aruch that one must marry by age 20. Nevertheless, in truth, it is possible even today for Bochurim to be mature enough for marriage by age 18-20, and hence fulfill the Mitzvah of Peru Urevu according to Biblical requirement, through educating them at an early age that they should expect to get married by that time, and so is done in many Chassidic communities until this very day. As stated earlier, the Rebbe strongly encouraged and advocated for early marriages, from age 18.
 Michaber ibid; Rambam ibid; Kiddushin 29b “Until twenty years Hashem waits for a man to marry. When he reaches age 20 and is still not married, Hashem says let his bones swell.”
The reason: As it takes up to five years to learn the [entire Talmud], and in previous times they would learn with the children five years of Mishneh from age 10 and 5 years of Talmud, which are the Mitzvos with their reasons in a summarized fashion, [and hence by age 20 they completed their Mitzvah of Yedias Hatorah]. Hence, since there is no longer a need to delay marriage past 20 years old due to Torah learning, therefore, one who went past age 20 without getting married transgressed the Biblical positive command of Peru Urevu. [Admur Hilchos Talmud Torah 3:1] Alternatively, as once one turns 20 years old he is liable for Heavenly punishment. [Aruch Hashulchan 1:11]
Other opinions: Some Poskim rule one may delay marriage until 22 years of age. [See Shaiy Lamoreh 1 that the Peri Chadash got married at 22, and this is based on opinion of Rava in Kiddushin ibid]
 Admur Hilchos Talmud Torah 3:1; Rambam Ishus 15:2
 Aruch Hashulchan 1:11
 Maharikash, brought in Pischeiy Teshuvah 1:5
 Rama ibid
 Michaber ibid; Tur in name of Rosh
 Rama ibid
The custom of Jerualaem Jewry: In Jerusalem, an institution was made that any man who reaches 20 years of age and is still single, must leave the city. This institution was enforced in previous times, and has been around for at least 300 years. [See Sefer Asos Mishpat p. 263; Hatakanos Al Yerushalyim p. 41 that the father of the Chida signed on this Takana, which was a reinstitution of a previous Takana. It is also signed by the following Rabbanei Yerushalyim: Author of Admas Kodesh; Peri Hadama; Get Mekushar; Rav Yaakov Algazi] In the mid 1900’s, the Sefaradi Yeshiva “Porat Yosef” experienced a series of tragedies, which the Roshei Yeshiva attributed to lack of enforcement of this Takana. They desired to remove the Cherem, although not all the Rabbanim agreed to do so, and it hence has remained in place. There is discussion amongst Rabbanim as to whether this Takana applies to all of Jerusalem, or only to the old city. [Heard from Harav Yaakov Yosef za”l] Practcially, Harav Yaakov Yosef za”l would rule for Bochurim who have reached 20 years of age to leave the city of Jerusalem and go study elsewhere.
 Michaber Y.D. 246:2; E.H. 1:3; Admur Hilchos Talmud Torah 3:1; Kiddushin ibid “Learn Torah and then get married”
The reason: If one gets married prior to learning Torah, he will be under financial burden to support his wife and children, and will thus be unable to study Torah as much. Now, although the one must stop learning in order to fulfill a positive command, this only refers to a positive command that can be fulfilled momentarily, as one can shortly afterwards resume his Torah learning. However, if one were to get married, then he would be unable to continue learning at all, as he must now sustain his family. [Admur Hilchos Talmud Torah 3:1]
 Beis Shmuel 1:5 in implication of Rambam; Rav Akiva Eiger 1 in name of Maharam Mintz 42
 Chochmas Shlomo based on Beis Shmuel ibid
 Rosh Kiddushin 1:42, brought in Tur E.H. 1 and Beis Shmuel ibid; Levush 1; Rashal Kiddushin; Aruch Hashulchan 1:13; Shevet Halevi 3:173; See Admur Hilchos Talmud Torah Kuntrus Achron 3:1 who learns in Rashi and the Rambam that the limitation is five years for Mishneh and five years for Talmud.
 The reason: As this allowance was only given to Ben Azaiy. [Rosh ibid] However, the Beis Shmuel ibid explains, that the novelty of Ben Azaiy is that even if getting married would not disturb him from his learning, such as if he is wealthy, he is still not required to get married.
 Rashal Kiddushin; Aruch Hashulchan 1:13; Sefer Hamitzvos of Chofetz Chaim “Until 25 years of age”; Shevet Halevi 3:173
 This includes all of the Jewish laws, all the 613 commands together with all their details, Biblical and Rabbinical, and their summarized reasons. [Admur Hilchos Talmud Achron 3:1] This includes even knowledge of those sections of laws that are not applicable, and are not practical, for all people, such as Kodshim, Zeraim, Nashim and Nezikin. However, one may not delay marriage simply for achieving greater depth of understanding and Pilpul in Torah. [Admur Hilchos Talmud Torah Kuntrus Achron 3:1]
 Hilchos Talmud Torah 3:1; See Hilchos Talmud Torah Kuntrus Achron 3:1 that one cannot delay marriage forever simply to further his in depth understanding of the Torah, as this is a study that has no end, and in any event one will never reach the final depth of his research.
 Igros Kodesh 10:202; 14:30 [printed in Shulchan Menachem 6:95]
 See the letter which was signed by Rabbinical leaders, Mashpim and Roshei Yeshiva’s from various Chabad communities.
 Shevet Halevi 3:173 [as soon as possible; age 24]; Chazon Ish E.H. 148 and in Peas Sadcha 1:149 [until age 20]; Rav SZ”A [until age 20], brought in Sod Hanissuin p. 73 [he married all his children prior to age 20]
 Michaber 1:4; Rambam Ishus 15:3; Ben Azaiy in Yevamos 63b; See Hilchos Talmud Torah Kuntrus Achron 3:1 that even the Chachamim agree with Ben Azaiy, and hence the Rambam and Michaber rule that one has the option of doing like him; See Aruch Hashulchan 1:14 that the Rif omitted this ruling and according to some Ben Azaiy did get married, and possibly it was literally Sakanas Nefashos for Ben Azaiy to stop learning Torah, and therefore he could not get married.
 The reason: As one has a constant Mitzvah of Yedias Hatorah, and if he gets married, and has no time to review, he will come to forget his Torah learning. Thus, one can choose to not get married in order so he review his Torah learning his entire life and not come to forget any aspect of it. This is why Ben Azaiy did not marry, as he feared he would forget his Torah learning. Now, although we rule that one must stop his Torah learning in order to fulfill a passing Mitzvah, this is only in a case that one can then return to his Torah learning, however if the Torah learning of Yedias Hatorah will be pushed off forever, then one is not required to stop to perform the Mitzvah. [Hilchos Talmud Torah Kuntrus Achron 3:1]
 Beis Shmuel 1:5
 Admur Hilchos Talmud Torah Kuntrus Achron 3:1
 Taz 1:6
 Aruch Hashulchan 1:14
 Hilchos Talmud Torah Kuntrus Achron 3:1
 The reason: See previous footnotes for reason in Admur.
 See lengthy explanation in Admur Hilchos Talmud Torah Kuntrus Achron 3:1 and how Admur learns this in the Rosh
 Implication of Admur Hilchos Talmud Torah 3:1 and Kuntrus Achron 3:1
The reason: One cannot delay marriage forever simply to further his in depth understanding of the Torah, as this is a study that has no end, and in any event one will never reach the final depth of his research. [Admur Hilchos Talmud Torah Kuntrus Achron 3:1]
 See Shevet Halevi 3:173 that erotic thoughts is defined as literally thoughts, evenb if it does not lead to sinful activity [i.e. Zera Levatala], as thinking such thoghts is itself Biblically forbidden.
 Admur Hilchos Talmud Torah 3:1-2; Michaber Y.D. 246:2; E.H. 1:4; Beis Shmuel E.H. 1:5; Taz E.H. 1:4; Rambam Talmud Torah 1:5; Kiddushin ibid “and if he is unable to be without a wife, he should first marry”; Based on Yuma 29a; Vetzaruch Iyun why it was not mentioned in Michaber 1:3! See Divrei Yatziv E.H. 3
 Igros Kodesh 13:23
 Admur Hilchos Talmud Torah 3:1
The reason: As only if one learns and remembers the entire Torah does he fulfill the Mitzvah of Yedias Hatorah, which is even greater than the Mitzvah of Peru Urevu. [Admur Hilchos Talmud Torah Kuntrus Achron 3:1]
The reason: If one gets married prior to learning Torah, he will be under financial burden to support his wife and children, and will thus be unable to study Torah as much, and will be unable to learn and remember all the Halachos with their reasons, which is the explanation of the 613 Mitzvos, and the main part of the Oral Torah. Therefore, the great Mitzvah of Peru Urevu is delayed due to this learning, even though it is the greatest of all the Mitzvos, as Talmud Torah is greater than all the Mitzvos and hence makes him exempt from the Mitzvah of Peru Urevu. Now, although one must stop learning Torah in order to fulfill a positive command that cannot be fulfilled by others, this only refers to a positive command that takes up a limited amount of one’s time, as one is only nullifying the command to constantly learn Torah. However, it does not refer to nullifying forever the Mitzvah of Yedias Hatorah, which is knowledge of all the Halachos and their reasons in a summarized fashion. [Admur Hilchos Talmud Torah 3:1; Kuntrus Achron 3:1]
 Admur Hilchos Talmud Torah 3:1 and Kuntrus Achron 3:1
 Implication of Admur Hilchos Talmud Torah 3:1 and Kuntrus Achron 3:1; Implication of Tzemach Tzedek in “Maaseh Chassidim Harishonim”, printed in Hilchos Talmud Torah [Ashkenazi] Volume 5 p. 645, regarding that one who cannot learn all Torah may lengthen his Davening as he is not applicable to the Mitzvah of Yedias Hatorah.
Tzaruch Iyun from other sources: Tzaruch Iyun from Admur Hilchos Talmud Torah 2:8 and 4:6 in parentheses which seems to imply that even one who cannot learn and remember all 613 commands in detail, can still fulfil the Mitzvah of Yedias Hatorah through learning and remembering the maximum of their ability. Accordingly, they too would be allowed to delay marriage until they fulfill their limited version of the Mitzvah of Yedias Hatorah. This contradicts the implication above that such people cannot fulfill the Mitzvah of Yedias Hatorah and hence do not have the above allowance relevant to them. See, however, the statement of the Tzemach Tzedek ibid, who seemingly learns in Admur 4:6 that they do not have an ability to fulfil the Mitzvah of Yedias Hatorah. Vetzaruch Iyun on how to fit all this into Admur. See Hilchos Talmud Torah of Rav Ashkenazi ibid who leaves this in a Tzaruch Iyun. See also Hearos Ubiurim 770 5764 for an article on this subject; See Shevet Halevi 3:173 who brings the ruling of Admur ibid and concludes that from the spirit of his ruling we can conclude that the allowance applies to anyone who desires to acquire knowledge in Shas and Poskim even if he will not complete it all.
The reason: As the Mitzvah of learning Torah is only greater than Peru Urevu if one can fulfill the Mitzvah of Yedias Hatorah, which is to learn and remember the entire Torah. If however one cannot do so, then although he can still fulfill the Mitzvah of Vehigisa Bo Yomam Valayla, nevertheless this does not push off the Mitzvah of Peru Urevu, as the Mitzvah of learning Torah is pushed off by any Mitzvah that cannot be fulfilled by others. [Admur ibid]
 See Shevet Halevi 3:173 “Who today can say they are clean from erotic thoughts, when the streets are filled with immodesty and promiscuity, and certainly it is obvious that one must get married as soon as possible.”
 Birkeiy Yosef 1 in name of Rabbeinu Yona in his Tzava, brought in Pischeiy Teshuvah 1:2; Aruch Hashulchan 1:11; See Igros Kodesh 29:272
 See Admur Hilchos Talmud Torah 1:3