i know what you mean on this one (@ original poster)
i have allways been big for my age (a good foot or 2 taller than the rest of my year at school and looked a fair few years older than i was... (i had a full beard by 14yrs) due to these reasons, i tended to socialise with people in the years above me whilst out of school... when i got kicked outta school and only had the option to go to college, i was again with people a fair bit older than me...
now i tend to struggle to get into the crouds and get talking to people my own age.. they just seem to chat about childish (sry, i cant think of a better word) things.. or things that you have no interest in...
now i'm older, its slightly easier.. in my case now, its frequently talk about football, and i have little to no interest in the game.. so i'm often sat at the side in silence, supping my beer, and staring out the window.
however, i'm slightly concerned now, that i'm going to Uni, and i'm going to be a good 5years older than most of the people who i'll be starting with.. the best tecnique is, if you dont have anything to say on a subject.. listen to what everyone else is saying... or ask questions regarding the subject.. you will gradually be able to atleast join in the conversation.. and you may even pick up some new interests/hobbies..