There is no "right age" for plastic surgery since everyone has problems or concerns that are specific to them. Many women elect to have breast augmentation in their late teens or early twenties while others have breast surgery after childbirth.
Weight loss surgery has become so popular and effective that patients of all ages are having body contouring of multiple body parts after massive weight loss.
In years past there were fewer options to treat facial aging but now women (and men) are electing to begin botox, fillers and skin care at a younger age to delay any need to consider surgery.
Prominent ears can be optimally corrected at age 5. So as you can see there is no such thing as a "right age".