Why should the patriarchs have lived to 180?

Question

Rashi to B'reshis 25:30 says that Avraham should have lived to the age of 180 had his life not been cut short.

Yitzchak lived to 180.

The Daas Z'kenim to B'reshis 47:8 quotes a midrash as saying that Yaakov should have lived to 180 had his life not been cut short.

Does anyone explain why they should have lived to 180?

Note that I'm not asking why they should have lived to the same age as one another (although that's an interesting question, too). I'm asking why they should have lived to 180 specifically. However, answering why one of them should have lived to 180 and why all of them should have lived to same age will serve as an answer to my question.

Answer 1

I have no source for this, but I would guess that it has something to do with the fact that the Torah calls Yitzchak "שְׂבַע יָמִים" - "full of days" at his death (Bereshis 35:29), a description not given to the other avos at theirs. This would seem to imply that Yitzchak lived a "full" life in terms of length, i.e. he lived as long as he should have and as long as he could have, as opposed to the other avos who did not.

[Edit: Similar statement found in Sifsei Chachamim 25:30.]

[Why they all should have lived the same duration is another question, as you noted. But once that is assumed, it seems reasonable that that duration should be 180 years, as explained above.]

Answer 2

Not (even close to) a complete answer, but the Etz Yosef, in his commentary on Bereshit Rabbah 63:13, says that we know as the generations went on the life span got less and less. If so, how could Yitzchok have lived longer than Avraham. It must be that G-d shortened his life.

Based on this, it would appear that the least amount of time that Avraham should have lived would have been 180, since that is how long Yitzchok lived. (There is no upper end to how long he could have lived, but we have no way of proving it was more than 180).

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The Midrash Tanchuma (Ki Teitzei 4) says something in a similar vein. It says Yitzchok, who comes "MiKoach Avotav" (the strength of his father) lived 80 years, while Avraham only lived 175. There must be a reason.

I'm not sure what the logic of 'comes "MiKoach Avotav"' is.

Answer 3

Not much of an answer to your questions, but perhaps a step in the right direction.

Maayana Shel Torah to Bereshit 5:5, brings from HaKtav V'Hakabala to Bereshit 25:7 that it says Adam lived the years "which he lived" to tell us that he did not actually live as long as he was supposed to, because he gave 70 years to King David. So the years that he actually lived (930), were not the days of his life (supposed to be 1000).

He then says that that's why it uses the same terminology by Avraham (Bereishit 25:7), because Avraham was supposed to live longer, but his life was shortened so that he wouldn't see Eisav's wickedness ( Rashi to Bereishit 25:30).

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So we know Avraham was supposed to live longer, but we don't know how much longer. It does not say "that he lived" by Yitzchok, which tells us that Yitzchok lived the amount of time he was supposed to live. We don't know until when Avraham was supposed to live, only that he was supposed to live longer. We therefore say that Avraham was supposed to live until 180, which was a complete life for Yitzchok.