I'm 38 and the wife is 39, and we're on our first (likely only) child.
I had a friend several years ago that had her first child at 40. She specifically told me not to wait that long, as it's a lot harder to handle all the stuff that goes along with a kid when you're older. Clearly, I didn't listen, and I'll have to learn the hard way.
I'm 37 and my wife is 39. Things will be interesting for sure.