Welcome to the forum!
It looks like the first two were answered (thanks Robyne!) but for (c) here is my opinion...
I agree that teen plastic surgery should generally be avoided, except for reconstructive cases. As you said, we all grow at different rates, and sometimes the breasts may not reach their full size until later.
The other concern I have is if a girl truly knows what she wants that early on. She may feel she wants a larger size, but does that means a slight increase or drastic (and fake) look? At the age of 16 or 17, the girl simply may not know. Take the nose for example... I was unhappy with it growing up, but didn't know what I wanted until several years later.
It also probably isn't the best idea to teach children that plastic surgery is the "go to" answer. First they need to mentally grow before making such important and life changing decisions.
I hope this has answered your question