I hit 28-29, after barely having a serious relationship for 6 years and out doing whatever I wanted, blowing all my money on food, drinks and friends etc.
It got old.
I got old.
I sort of realized that if I was lucky enough to stay relativity healthy, a 1/3rd of my life was over, and what was I going to do with the rest of it?
I didn't really 'think' of like 'how I need to have some kids now!"....it was more of a 'i think I'm ready to move on to the next stage of my life.'
For me, the next stage of my life logically involved having a family...but it was also about having a long term relationship and the stuff that came with it. My older sister had kids young and was and is a fairly lack luster parent. I know a couple who were having some problems and thought a kid would fix it and it is now a divorced situation and a floating kid who they both love, but don't put first.
Everyone is made to have kids, but not everyone's made to raise them