Even people NOT on the spectrum are waiting later to marry and start families. People are more adamant about their educational and career goals that they don't have time for serious long-term relationships. TBH, I think waiting later is a bad idea. It is true that pregnancy is riskier at later ages. And I think relationships are tighter and more productive with time. I think there's a bit of a learning curve you overcome with age, so older couples in new relationships have an easier time starting out knowing what they want and expect from a partner. When you're young, you often don't even know what to expect from YOURSELF, much less someone you love. But then when you have that opportunity at a younger age to not just grow up and become a responsible adult, but you join someone on their own journey, I think the later years are much more meaningful.
I'd honestly intended to marry my h.s. sweetheart and was set for it. But after 6 years from middle/high school to mid college (she was a year younger than me), and having to deal with all kinds of things along the way--the death of my father just prior to dating her, having to deal with a stepfather who...ok, wasn't really all that BAD, just not very nice to ME...school bullies, and really just one thing after another, and not even really a very good college kid, and discovering that YES, some college girls DO notice me--everything fell apart. Sure, I'm grateful for the life I have now and am glad things turned out the way they ultimately did with 4 kids and the wifey wanting one more. But it shouldn't have to be that hard, and maybe things would have gone better had things been easier without all the pressure to achieve this thing and that thing, get rich, buy the house, buy the car, and THEN get married. Well, heck, NOBODY would ever get married if that was the reality. My wife and I also waited a long time, though I was 27 when we got married. So we didn't exactly wait until our 40's. But we're in our 40's still having babies. I'm glad that we had over 20 years of history, and that makes this experience that much sweeter.
I'm not saying waiting is necessarily all that bad, but waiting that long just isn't right for me.