I don't think it's out of line for him to question your reasons for the surgery if they are not obvious (I didn't see you write anything about being in pain). My concern would be why you're having the surgery since it is pretty major surgery and there are some consequences (years ago you couldn't nurse a baby if you had surgery, but I don't know if this is still the case). Plus, you are very young and it is possible that your reasons for the reduction now may not be the same years down the road.

That said, he should never tell you what to do. It's your body and men need to understand that they aren't in positions to tell women what to do with them.