What do you think about age difference?

well what can i say lifes pretty good but i got things that bother me like everybody else and what bothers me the most day to day is age. The reason for this is im always hanging around people much older than me. My best friends are 18 and 19, one being my cousin that ive been around my whole life and his friends so ive been older kids but my other best friends was friends with my cousin and thats how we got to be such good friends just a year or so ago. Alot of times im hanging out with people who are 18 or older which i get treated fine cause ive always been around older people and im much more mature than anyone my age.. but when they find out how old i am i feel like in the back of there mind they think about it or blame it on me when it comes to something you might need to be a adult for. By the way i'm 15 almost 16 but it just bothers me to know when i hang out with 22 or 23 year olds that im being judged in the back of there mind even though we get along good and talk just like anyone else. I always seem to be the youngest one now in our group of friends used to be at the bottom but we hung out with some younger people. But i mean i feel like lifes good when i step back but i cant get the age out of my head it makes me feel like im not worthy. I mean if i party with them or anything else i feel like im really looked down upon even though most of them are underage for that too i guess but partying isnt my whole life like some people. What do you guys think? does this ever happen much? is it a good or bad thing?