12 strikes me as young. I had a friend in HS who needed breast reduction because it was causing her back problems and psychological harm as well. I think parents in consultation with doctors can figure out the right age.
Fine. 15 years old and wants the complete works. Breast implants, Lipo suction, lip and face filler. Would you support that? Again I ask, when did encouraging people to be ok with their own become taboo?
Also, your analogy represents primarily relieving physical pain.