My mom was 21 and I am an only child - she had major surgery after me and could not have more children, though I know she would have liked more.
I was 24 with DD and 26 with DS - at the time the doctors considered me "older" for having a 1st baby!
DD was 36 with her first - wish she had been younger, but she is a wonderful mother. She wants more but will be 38 in March and who knows who old she will be with the next baby. I worry about her being older with a second baby, but lots of women have babies at that age now and have healthy pregnancies and babies.