Basically
1) women are healtly fertile between 18-35 years (18 for social convention, biologically it's from 14 years)
2) women start to gradually lose fertility from 35 years, and are almost infertile by 40 years
3) to maintain a stable population, in normal settings, each woman should aim to have at least 3 kids (anything less than 3 kids each woman, means loss of population between generations)