It's logical from a financial perspective for many people. When I think of older first time parents I think 30+. In the past upper 20s might be considered older because people would get married in young 20s and have children shortly after.
You want to be able to afford the increasingly higher costs of having children. You want your marriage to not be stressed from added financial responsibility. People tend to make more as they get older so many wait. That played a role in my decision to wait for sure.
The physical component you suggested is certainly a logical argument for having them younger. That pressure is higher for women too because they consider the risks of pregnancy (as you noted) and the possibility they may not be able to conceive if they wait too long.
I understand your decision but to me - having a kid at 30 over the physical concern is not logical. Sure I'd be 48 when they're 18 but even at that point, I don't have physical concerns. In fact, that would provide additional motivation to remain healthy. If I was considering physical capability for grandkids then that might enter my decision. My wife just talks about how we'd be the older parents in our kid's class which doesn't concern me.
Everyone's situation is different though. I just think finances is a big driver for those that wait and honestly I think it's a good one. If you're married and don't have your finances in order, there's a good chance your marriage won't last and you'll rack up more stress which isn't good for you or your kids.