text: I agree with your doctor, you're only 15 now, your hormones are all over the place, and your chest will need the extra space once your upper body muscle starts growing in....but...\n\nIf you have to ask this one again at 18 or 19, I'd go to a doctor, have my blood tested for hormones.  Really.  Hypo-gonadism is no joke, and neither is hypo-pituitary syndrome.  You did say you were tall though, so if it continues to be an issue in 3-4 YEARS from now, check to make sure your body is producing enough testosterone.\n\nYou may, if you can afford it, also wish to have a combined blood/sperm test for chromosomes....a small number of guys are born with Klinefelter's syndrome, which basically means they get an extra X sexual chromosome, being an XXY male instead of the normal XY.  But that is really rather rare.\n\nAnd like I said, you are too young to sweat it now....give it a few years, if you find yourself having chest/breast issues as you get closer to 20, that is when you need to look into it.