How old do you have to be to get fat transfer to the butt ?

Hello dear!
Thanks for the question and provided information as well.
You should be at least 18 years old to be a candidate for plastic surgery.
In general, you need to be physically healthy and at a stable weight, have realistic expectations, be a non-smoker and your BMI needs to be 30 or less.
l recommend you to make an appointment with a board certified plastic surgeon to talk about your goals and anything you need to know.
Good luck :)

Assuming it is for cosmetic enhancement, most surgeons would recommend the patient be at least 18 years of age. Glad to help.

You have to be at least 18 years of age. There is not age limit thereafter as long as the patient is healthy and a candidate for surgery.