[WalterBright]

Delaying having children until ones' 30s also is a problem. After 30, fertility rates decline, and birth defects increase. You can't have a lot of children after 30, either.

[vardump]

I think steeper decline is at about 37ish years for women.

There's also some deterioration as men age, but it's less obvious.

Some say the combined age should not be over 80. Shrug.

(Should be obvious fertility varies greatly between individuals.)