Just because other girls wear it, that doesn't mean you need to. 13 is a good age to start wearing makeup. You don't need to grow up too fast, or attract unwanted and dangerous attention from boys who are too old for you.
Just because many other girls are doing it at school does not mean you should. 11 year olds should not be worrying about what make up to wear, go and spend your money on some cd's or something.