Actually, my question is this. GIVEN that man once lived up to 900 years and more. WHEN in his chronological life did he become old, as in feeble and not physically productive? Assuming the women were also long-lived, when did women go through the change of life?
I think it’s likely that people aged far more slowly in that time. According to the generations passages, nobody married until they were over 100 years old. That may have been as soon as they reached maturity back then.
Even now, there’s a rare genetic problem in children where they age very very slowly, but is usually fatal, probably because it’s combined with all the other genetic mutations.