Hey, I'm, uh, 40 or so too! Heh.
Born in '65 (in US, natch - east coast), and...
yesterday was my birthday! (honestly!)
Beatles were still major, of course -- as my mom scribbled in my baby book....
Until ds (age 3.5) was born, my day job was science lab stuff on college campuses -- so even though I kept feeling normal, my co-workers kept getting younger and younger (except old git professors 
). Gradually started mildly freaking me out to wrap my brain around the fact that many of the people I worked with weren't even born yet when the first Star Wars movie came out, much less before anybody landed on the moon....
And I'm in pretty good shape. All the walking about while living here without a car (and having a 2nd/3rd floor walk-up flat, and nobody (incl. dh) to throw back pints with (yet!) is keeping the waistline better than it'd been for a long long time. The reason Americans are so @#$%! fat generally is because nobody walks anywhere and everybody drives everywhere because everything's too far apart and there's no mass transit practically anywhere except the densest parts of the biggest cities. Which isn't where most people live.
And a lot of my friends from home/school/etc. waited a while to have their kids, too, so at least among most of my mates back home, we're all in the same boat age-wise. Except for one, who had ds & dd in our early 20s and the kids're nearly out of the house now! There're pros & cons both ways, I guess. Don't know if I would have swelled up like a @#$%! toad while pg or not, if I'd done it in my 20s instead, but it still worked out all right for me, fortunately. In my family, at least, the women generally don't do menopause until they're in their 60s... dunno if that's a good thing or a bad thing!