In addition to what the others have said, it's less painful and easier to have done when younger. This is like saying parents shouldn't be allowed to make kids go to school, they should wait until they're old enough to make the decision themselves. Sometimes parents need to make a decision for their children, it's only logical.
It's not bullshit at all. Let's look at it a different way. If a child has some physical mutation such as webbed feet, an extra finger, or some other physical difference that they wouldn't affect their health, you're telling me a doctor shouldn't ask if a parent would like to have something done about it and instead the child should grow up with that until they are old enough to give consent? When is a proper age for consent?