I haven't really put a number on it but I guess 40ish would be my cut off I guess it depends on how life goes
I had my first at 23 and second at 24 and feel I need a rest for at least 6 years while I study but dh is finished I could go another though so were looking into maybe adopting or surrogacy given the issues I've had from the last 2 pregnancies who knows I'll study and work a bit and see what's going on at that life stage I'm only 26 so I feel no rush