I'm 28.
I don't think of it as depressing. Yes there are social activities which are fun to do as a group. I do meetup with my ex-schoolmates at least once a year for old times sake. But other than those instances and occasional outings or trips with my family, I prefer doing things on my own. I don't mind when people come up and talk to me at work or when I'm outside. I will try to engage myself in their conversations. Otherwise, I don't go out of my way to socialize.
Well, this is me. Now. I might change 10 years down, who knows. :)