> if 80% of women are done with children by age 30

Is this assumption based on anything? Not saying you're wrong, after all the majority of the world's population live in poor countries where people have children younger. But at least In my social circles it'd be more accurate to say 80%+ of women start having children at age 30 (or later) then are done with it. And I know multiple women who had their first child at 40+!