of course, it's never too late for anything, as others have already suggested. if it's something you want to do and feel like could be a good experience for you, then go for it, never deny yourself anything because you feel others will look down on you. dancing is so much fun and can make you feel incredibly free. ballet (my favorite, kudos for selecting that, btw) is an especially beautiful and expressive form of dance and a skill that you can look back on and cherish forever.
HOWEVER, most people do start very young, i began dancing at 2...and although this is rarely an indication of how good the dancer is (more often it is the studio they went to, level of talent, and commitment), the way ballet works it is very hard to break into as an adult. you are still young and can do this for years still, so don't worry about that, but it will be harder for you and you probably won't get into the higher levels even by the time high school is over (depending on the studio you select), so if you are planning on being in performances of any kind, keep this in mind...you may very well be subjected to feeling foolish among much younger girls for awhile. not that this means you shouldn't go for it, but keep that in mind.
also, since your body is probably developed already, your muscles might not be used to this kind of movement so be CAREFUL. when stretching do not let your teacher push you down further than you can go without hurting yourself because it could cause you serious injury. and don't be convinced to go on pointe until your feet are strong enough, even if you are old enough.
finally, don't expect to be awesome at it right away, it takes lots of time and the girls in the upper levels will have been taking dance for upwards of 10-15 years already. if you are very competetive, this is something to think about, but it sounds like you're not. just don't feel embarrased. power to you for taking this initiative.
i hope you do decide to do it, because it's a life-changing experience if you get into it. keep your movements soft and really commit to it and you'll get where i'm coming from when i say you'll feel like you can fly. or like you're a princess :)