First, how old is he? If he's under 40, then he sounds "high maintenance" about his appearance and that smells like trouble to me. Most guys think they look great with their four strands of hair combed over their bald spot and their beer bellies hanging over the tops of their sweat pants.
Second, you need to try to ask him gently why he feels the need to have this stuff done. If there's an older relative (dad, mom, grandparent) with the double-chin, he might think this surgery could prevent it from happening to him, but there are no guarantees. Assure him you love him and will always love him no matter what.
Then, remind him that beauty is only skin deep anyway. We all age -- get wrinkles, sagging skin, thin or graying hair, whatever. This indicates maturity, experience and hopefully wisdom from having lived life. To look your best at any age, eat right, exercise and take care of yourself.
If he really is that self-focused on his appearance after all your efforts and seems dedicated to this course of action, be prepared for this pattern to continue and decide if that's what you want to deal with in your future. I hope that this all works out for ya! Be supportive and listen to what he says when you ask.
-Dorothy (LadyZolt)