This. I was in a fandom for a long time where a lot of fans were in their 30s and 40s, and even the younger fans I was friends with tended to be my age or older. Now, I'm getting into another fandom, and have been a bit surprised at the number of people around my age and a little younger (that is, "college" aged).

I like having people in fandom who are a different age than me, though. I don't think there's a "right" or "wrong" age.