My wife and I were married when I was 25 and she was 23. I just turned 30, and while back then I was all about having children, I'd like to put it off as I still have a lot of places to visit, things to do, etc.
She, on the other hand, is ready to have children. Now. Since she's 28, she has a plan to have X kids, spaced X years apart.
The next 6-12 months of our relationship will be interesting.