I wanted to have children before getting married. However, I married late (in my late 30s).
OP, don't worry. At age 31, I also wasn't yet in Daddy Mode. Probably by age 33, I had enough children and dads around to realize something like, "if my pal Stoney (the former grunge slacker) can handle kids, there's no reason why I can't do the same or better."
As an older dad, I see a trade-off. The benefits are that I'm more settled in my career and can parlay the observations and experiences of good parents around me so everything isn't new or a huge challenge. And as you approach and attain middle age, you should have a more mellow or wise approach to things.
The downfall is that you don't have the energy you did in your 20s-early 30s to keep up with kids, and thus you might not push as hard for things as you once did or let some things slide that sometimes you shouldn't.