I know exactly how you feel. There are, I'll admit, quite a few ways in which I'm less mature than my classmates. Many of my friends combine my behavior with my height and petite-ness and like to tease me as if I were seven, which I'm fine with for a joke or two, but when they actually treat me like I'm a kid, it very annoying. The best thing I can say is to find a friend who really understands you and knows the difference between behavior and intelligence. That friend would definitely help whenever you feel annoyed or aggravated my others.