According to the Talmud in Megillah, and quoted in Rashi at the end of Toldos, Yaakov was 84 when he first married. Why did he wait so long?
I saw somewhere (don't remember where) that Avraham first married at 65, and the verse says that Yitzchak married at 40. And it seems that by Yaakov's time lifespans were much shorter, so it's surprising that he remained unmarried for so long.
The Maharam Shik posed this question in the first teshuva on Even Ha'ezer. (See the second and third paragraphs here).
He says that the Avot wanted to have holy descendants and therefore delayed the mitzva of 'peru urvu' until the time that they could find the most suitable spouse.
Generally, one is allowed to delay the fulfilment of a mitzva if one will be able to fulfil it in a better way at a later time. However, he cites the Terumat Hadeshen to point out that this would only allow a delay of a short time, and in this case the delay was a matter of decades.
Therefore, Maharam Shik explains that usually one has to worry that something might happen in the meantime that will prevent the person doing the mitzvah. In the case of marriage, the person might die before they get married (think Nadav & Avihu). However, the Avot were guaranteed by Hashem that they would become a great nation and so that concern did not apply to them.
R. Avraham Ben Harambam writes in Hamaspik L'ovdey Hashem (ed. Wincelberg pg. 369) that this was due to his pious asceticism:
For this reason, one who aspires to this lofty way should embark on it before he has a wife and children who might distract him from spiritual pursuits. Doubting one who plans to marry and then involve himself in Torah study, our Sages said, "A millstone is on his neck, and he will be immersed in Torah?" (Kiddushin 29b)...Our forefather Ya'akov did not marry until he was 83 years old (Megillah 17a).
He doesnt address why Ya'akov got married somewhat later than Avraham, and Yitshak, but rather notes in his commentary to Genesis (24:1) that the forefathers in general got married late since they wanted to first pursue spiritual objectives.
