I didn't answer the age question because my friends range from highschoolers to people in their late 50s, though most of them are probably somewhere between their late teens and their late 30s.

I don't really have any non-fannish friends and haven't in many years. The only difference is that these days I know most of them through fanfic fandom on the net while back in the day I knew them through science fiction fandom organisations and cons.