If I had a teen-aged daughter who wanted a breast reduction or mastectomy, and we decided it would be the right thing to do, and the doctor decided it would be the right thing to do, we'd do it. Especially if she is being sexually harassed because of her breasts. No waiting until she's 18, because the harassment is occurring NOW, and will likely continue after she becomes an adult. If some self-righteous authoritarian politician wants to pass a law prohibiting her from it in the name of protecting her from abuse, then you can expect me to do everything in my power to prevent the State from interfering in our private medical decisions. Especially if the breast reduction was to stop harassment and abuse she might be experiencing because of her breasts. (Not to mention avoiding future breast cancer.)
Politicians are not doctors. Doctors are not lawyers, and should not be intimidated by politicians who don't know squat about medicine making asinine laws prohibiting sound and beneficial medical practices.
I think we ought to put breast reduction in a different category than mastectomy. There are HUGE differences in the long term consequences of those two procedures.