Sometimes, it's kind of weird when your older friends have kids... and they look a lot like your friends. "OMG, she looks just like So-and-so when I first knew them in school" or something. A few years ago, it seemed many friends were getting divorced, too, and I realized, "Gees... many of my friends are going through their first marriages... and look at that, in their early 30s. That sounds about right."
I once posted this on a board, and an older poster said, "Just wait until your friends start to die..."