I've been thinking about the "fitting in" issue, too, though I'm approaching it from a different perspective--five years out of undergrad, married for almost three of those. I think I have learned something in that time, and I value the experiences I have had. I think my work experience in public policy will be especially good as I head into this realm of the unknown.
With all of that said, I'd like to counter the idea that married people (or "older" people) don't like to hang out, go out, or have fun. True, I'm drunk less often than my senior year in college, but I consider that to be a big plus.

And, I enjoy a good party or a good night out as much as I ever have. My spouse and I definitely like to hang out together (what's the point, otherwise?), but we're still pretty fun people who lead somewhat independent lives.