Here's a funny thing: sometimes people have a real go at me and my friends without kids, for the mere crime of being 36 or 37 and not having reproduced yet.
A woman started in on my married but determinedly child-free friend, who is 37, calling her "selfish" and all those old chestnuts.
Then, a random guy started in on me, too, and his friend - it was like open season once they'd discovered I was 36! Your age is like an invitation, it seems.
Anyway, I have an excellent and comical response all ready. When people tell you that you're selfish/self-involved/whatever other insult, you just agree. So, to the obnoxious guys, I just cocked my shoulder, flipped my hair over it, and said, "Yes, I am, I'm completely selfish and evil and I LOVE it!" They seemed to get the point and they really laughed, and after that I didn't get any more hassle.
If someone starts on you, just agree. I told my friend that she should have told the baby-crazy harpy: "Well, of course I'm selfish. Who's more important than me?" Hahaha! Then, they have nowhere else to go with their argument. Once you start defending yourself to these people, you're sunk.
My mother nastily sniped at me once, when I said I wasn't sure I wanted children, "Oh, you'll grow up one day." I just said, "Really? You sure? I wouldn't count on it!" She laughed. (For the record, I was 32 and married at the time. Such is the familial nastiness I experience for not having reproduced yet.)
I wonder if these people ever realise that it may not be a good idea to hurt, isolate and anger someone who (as far as they're concerned) might be the mother of their grandchild/niece/whatever one day....