First child? Around mid-twenties to 30. In my circle. Various circs, some professionals and homeowners, some not, it differs.
I don't know that many who have children in their mid-30s to 40 and only one who had her second at 42, but she is seen as a bit crazy for it, have to admit.
I had mine at 24, she's 12 now. Only child, don't want more. I went to uni, have my own business and own a house, so my child certaily didn't stop me (or my friends).
I'm 37 now, DD is 12, needs way less active, hands-on parenting as a baby/toddler does. I can do whatever I want to, we travel lots together, go to gigs, days out, etc. Life's good.
There's zero chance I'd want all the night feeds and running after a toddler now. And I'd rather poke my eyes out than do it in my 40s. All my friends seem to think the same.
Although obviously I don't think anything about people having children in their 30s, to each their own and all that.