Speaking of genetics, I knew that I wanted to have children as early as possible in my life given my family history.
With my mother dead at 50 (cancer - I was 20) and my father totally mentally and physically debilitated post-stroke at 55 (I was 24), I figured the sooner I had kids in life, the better.
Even so, I still ended up waiting until I was 28 to have kids.  I had just gotten married at 26, so there wasn't much opportunity prior to that.  My wife was 24.  I figure that gives me better odds of my kids having an intact parent into their adulthood.
(Granted my grandmother just passed away at 99...but still)