As with most medical queries, the answer is...it depends. It depends on the procedure, and it depends upon the patients' development, maturity, understanding, goals, and reasons for seeking surgery in the first place.
Patients and sometimes parents desire surgery to correct under development or over development and to improve self esteem. There may be concern for or even a prior history of teasing at school.
The range of procedures is wide and includes more minor surgeries such as removal of moles, skin tags, or cysts that are on the face to correction of ear deformities, nasal deformities and breast surgery (augmentation, reduction and male breast reduction for gynecomastia).
For younger patients under the age of 18, it's very important that both the parents and the child are on board. If the driving factor is the parents and the child themselves isn't bothered by it then it is best to leave it alone. So how do you know when your child is ready? They will bring it up to you or you can ask them directly if that mole or blemish or ear shape bothers them and they will likely answer you honestly. Surgery is much more successful and the post op recovery is much easier when the child was the driving factor behind seeking surgery.
Conversely if the child is really into it and the parents are very hesitant- this can be a set up for disaster and regret. While most young patients can understand the immediate implications of surgery on their lives, they cannot comprehend or process the long term implications. They just don't have the life experience to piece it all together.
The first foray for parents into childhood cosmetic plastic surgery is likely the correction of prominent ears. This procedure is best done when the ears are fully developed (at least age 6), the child and not the parent is the one seeking the procedure (aged 8-17) and the child is ready to handle the post operative dressings and head band that are required. These criteria aren't typically all satisfied until around aged 9 or 10.
Rhinoplasty or "nose jobs" may the next cosmetic plastic surgery procedures to address along this chronological path of young patients seeking cosmetic improvements. Though rhinoplasty is very frequently done in very young patients with cleft lips, this is a procedure best addressed when patients' faces are no longer growing/changing. This is typically 14-16 in females and 16-18 in males. Nose size and shape should be proportionate to the individualized facial skeleton and this is difficult to achieve before growth has completed.
These examples demonstrate the importance of waiting until patients have reached physical maturity but fail to consider the importance of mental maturity.
It is the difficulty in evaluating mental maturity that makes deciding if a patient is a good candidate for cosmetic breast surgery perhaps the most contentious and controversial.
Undertaking these surgeries in young patients should be done with great caution. Unlike ears and noses which reach a distinct physical maturity and do not change over time, breast size and shape will fluctuate many times over a woman's life. There are changes associated with weight fluctuations, hormonal changes, pregnancy, lactation,and age.
This means that unlike a rhinoplasty result which will stand the test of time, the outcomes of breast contouring procedures such as reduction, augmentation and lifting may not last.
Secondly, the resultant scars in a young patient who has not likely found their life partner (i.e. stable long term relationship) create a new source for self-consciousness. These scars, which are permanent can be just as debilitating and destructive to confidence and self-esteem as the initial concern for breast size and shape, particularly following breast reduction and lifting.
With breast augmentation at a young age , the skin envelope may stretch to a point that if he implant are removed in the future a secondary lifting or tightening procedure may be required. Furthermore with age and particularly with the stretch and subsequent deflation after breast feeding the implant may not be sitting in the correct position relative to the breast tissue. This may also necessitate further surgery. Lastly, although there is no set expiry date for which implants need to be removed/exchanged, it is known that typically most patients have had some type of re visionary procedure for one reason or another within 15 years of their original procedure. It is therefore imperative that a young patient understand that in all likelihood she is signing up for more than one surgery related to the implants over the course of her life.
With all that said, there are some patients who may still remain good candidates despite their young age. A board certified plastic surgeon should be able to determine if the young patient has the mental maturity to appreciate the procedure in all its scope.