I dont know if he likes me?

Girl back out while you can before your heart gets broken into tiny pieces. With you being 17 and he's 21, yeah that plays a major part in it. If some people think something() is going on between you two, then they will report it and he can get into big trouble. He is just being friendly towards you. NOW WAIT: There is nothing wrong with him giving you his phone number. There may be a specail reason why he hasn't given you his phone number and he just won't tell you why. But yeah, you should back out before your hearts gets broken.