I agree - I would seek a second opinion and get a more secure diagnosis.
I believe the earlier the intervention, the better - for just about anything.
I know that our insurance only covers treatment for PWS on face/neck. Anything else is considered "cosmetic." However, our doctor's office told us that if we had trouble with our insurance company covering the charges they would advocate for us, as treatment for PWS is considered reconstructive. So if indeed you decide to treat it, your doctor's office may be able to help get it covered by your insurance.