Well Ken I'm 38 and I don't have it. I get more than enough social interaction right here. I don't really think of Facebook, My Space, Camo space, or any other space as immature, only some of the people using them. I wouldn't think any less of someone that used it, I just don't have time for it and I honestly don't want to have time for it.
I see some people on it so much that they loose the ability to relate to people on a face to face basis. I also hear that a lot of people share information online they normally wouldn't.