I am 19, my daughter is 7months old. Before my daughter was born, I thought 100% that I was too young, even though my fiancee' is 21. But now that she's born and I realize how much fun she is and how much I care for her I don't think I'd have it any other way. Sure I'd love to have a better job, and not be in school full time, its rough I'll admit, but every time I think about her (which is constant) I smile and wish I could be holding her.
I think the perfect age is like what Anthony said, between there and 25, no later. My dad is only 43, my mom 42, and they party harder than I do. (Sad I know). But the point is they're not too old to hang out with. We drink, we water/snow ski, we do things together, its great, and they absolutely LOVE my daughter, they can't get enough of her.