my dad was 45 when I was born and 47 when my brother was born.
maybe he didn't have as much energy as some of the younger dads when I was a kid. but on the other hand he was able to retire while I was in high school, so he was able to spend a lot more time with my brother and I before we moved out.
I am a bit worried about having an 18 year old and being 68 though. We'll see how it goes.