As a teenager I said I'd be done by 25 so I'd have no pre schoolers by my 30s.
Had 1 under 25 and it was very easy physically. I'd still done plenty of partying & travelling so I get a bit annoyed at those kind of comments about having DCs in your 20s.
I then moved limit to 30, so they'd all be in school by 35.
But a whole load of life stuff has got I the way, a few years have slipped past so now I'm pregnant with dc3 at 34. The timings still not ideal but I really didn't want to take the risks associated with being over 35. I don't want to go down that difficult antenatal choices path.
Also my parents (born in 1940s/50s) had mums who were 36 & 40when they were born. One died when parent was in early teens, the other didn't survive long enough so see me finish school. I feel like I've really missed out not having any grandparents as an adult.
However we would still maybe like another one. DP said before that him being 40 was his cut off. I wouldn't want the double nappies/double buggy life of a small gap but I wouldn't want to leave it too long either so I'd say the new cut off is 37/38.
However as it ekes getting pushed back it would surprise me if in 5 years I come back and say 42 is my new cut off!
I would never go down the ivf etc route though.
Round here 40 is a normal age to have a DC. About half the women I went to school with, now turning 35 haven't started having DCs yet so I imagine a lot of them willbe having DCs into their 40s.