I can totally relate to what you are saying. Our daughter just turned 8, and still I occassionally have those moments where I wonder why I ever became a mom. I absolutely adore my child, would do anything for her, and do love being mom, but it was something I had never considered when I was younger.
One of my closest friends is the mother of my daughter's best friend. I'm old enough to be her mother, in fact her mother is the same age as my husband.
Man, this sounds familiar. My wife and I married late and had kids late. I'll have kids in college when I'm in my 60s.