1)
Why does the Torah emphasize that the people of that generation gave birth "after the Flood" (surely, that is when they lived)?
1.
Ramban: To teach us that, bearing in mind that, the earlier generations had children at the age of around sixty, HaSh-m deliberately postponed the birth-age to above a hundred until after the Flood, either to minimize the number of people who would die in the Flood, or to avoid having to rescue more people that necessary from drowning in it. 1
1
Indeed, the Ramban adds, it is for the very same reason that HaSh-m postponed the age at which Noach bore his children, as Rashi pointed out above (See Bereishis 5:32).
