This is what the Beijing Institute of External Fixation Technology says in their FAQ.
Q: At what age is it possible to undergo the cosmetic height increase procedures?
A: The age of patients may be from 16 to 45 years, in rare cases the age limit can go up to 50 plus years for combined lengthening and deformity correction treatments.
Q: I am a 50 year old male. My height is 154 cm. I would like a maximal lengthening (170 cm up). Is it possible to
undergo the cosmetic height increase at my age?
A: The age for cosmetic leg lengthening is usually between 18-45 years old, the younger the better. However, Dr. Xia has performed cosmetic lengthening surgery in several cases for patients older than 50 years. For the older patients, the healing is bit slowly and we may lengthen at a slow rate, this means that you may have to stay in our hospital for longer period. But this can be done; we can also perform plastic surgery to remove the scars after the lengthening procedures (at reasonable costs). In your case, we will recommend you to come to our hospital and accessed by Dr. Xia in person, we can decide from there, as it is unfair for us to promise you anything at this stage.