18 Years Old. It is an elective procedure, so you really should be at least 18 years old (a consenting adult) to legally give your consent for a lip augmentation.
Lip augmentation age. Is this for cosmetic reasons, or did you have an accident or congenital defect that caused you to have lip asymmetry? If for aesthetic reasons, 18 yrs is generally accepted, although many providers would reserve elective intervention for an older individual. If p/trauma there's no age limit. The key is to preserve oral function for speech, swallowing and protect dentition.
No minimum. There is no minimum age for lip augmentation, however, this is a medical procedure that is elective and has some pain involved. In general i prefer the patient be able to give their own consent. In most states this is 18.