I'm 25. FB originally came out when I was in college, just geared towards college kids. I actually use it rarely. It's nice to read what my friends are doing (when you log in, it gives you a list of what everyone's doing), but I don't love how it's changed since I was 18.
One thing I would suggest is be careful about what you put on there. People are like "FB is giving out my phone number! Invasion of privacy" and I want to say to them "ummm, just don't put your phone number on the site. Duh" things like that