Could there be a way to stay looking a certain age forever ? Read below

According to yahoo News,  In the picture is Gabby Williams a 8 years old that has the skin of a newborn and only weighs 11 lbs. An ultra-rare genetic condition, for which doctors have no discernible explanation, keeps Williams from physically aging and has her parents caring for her nearly the same as the day she was born.
Williams shares her rare condition with only a handful of people around the world, including a 29-year-old man from Florida who has the body of a 10-year-old and a 31-year-old Brazilian woman who appears no older than two. While the medical community hasn’t yet established a cause for Williams’s or the others' conditions, research into the genetic disorder has promising implications for overcoming the inertia of aging.
 well the interesting assumption about this disorder is finding the cure and being able to fine the gene that is causing this disorder, Doctor Williams states "If we could identify the gene and then at young adulthood we could silence the expression of developmental inertia, find an off-switch,” said Walker, adding that “when you do that, there is perfect homeostasis and you are biologically immortal."
Well, everyone wouldn't that be great being able to stop the gene and being able to look the age you wanted too ? I would stop the gene at the biological age of 21, then being able to look 21. what age would stop the gene ?