I absolutely understand how easy it is to become a child again at WDW! We, too, will be visiting this summer with our sons, one of whom is nearly 15. We have made dinner reservations at Chef Mickey's because we like eating with the classic gang of Mickey and his friends, and our oldest son can survive that character interaction pretty easily. He also enjoys all he can eat shrimp and the sundae bar for dessert!
A couple other ideas are some character breakfasts. Cape May Cafe (Yacht/Beach Club) has one with a small group of characters: usually Goofy, Minnie, and Mickey. Tusker House in the Animal Kingdom has another with Donald, Daisy, Mickey and Goofy. What is nice about this is making a reservation before the park opens and getting to walk through the Animal Kingdom with few people around. Then, if you time it right, you can finish up breakfast just as the park opens. Grab a fast pass for Kiliminjaro Safari that is right next door and then head straight to Expedition Everest if your son wants to dive right into a FAST ride with little to not wait. Finally, 'Ohana at the Polynesian Resort has Lilo, Stitch, Pluto and Mickey. Your son may have fun with Stitch who has a few "teen" moments himself.