The thing that's starting to get me is that I know several people who are having babies in the near future (or had them recently). The ones having their first child are 3-5 years younger than I am, and the ones about my age are already on at least child number 2. I don't have any children, and don't expect that I will for at least a couple more years. Part of this is my own angst about the fact that I thought I'd be in a position to have my first child before I turned 30 (and I'm now halfway through my 30th year). But I'm also realizing that when I do have children, I will probably be the oldest first-time mother I know roughly 95% of the time.
That said, I don't actually think of myself as old at all. It's a little odd to be 30, but I realize that I'm still pretty young in the grand scheme of things. After all, all of my health care providers are still older than I am, and have yet to work for someone who is younger than me.