It's tough for me to recommend omitting
any of the theme parks from a guest's itinerary, but...for you, I will.
I'm operating under the assumption that your 12-year-old boy appreciates thrill rides as much as the next. With that assumption in place, I would suggest you cut Epcot and Animal Kingdom out of your touring plan and focus on experiencing as many of the attractions at Magic Kingdom and Disney's Hollywood Studios as you can.
I recommend Hollywood Studios because my own 12-year-old {girl} is crazy about the attractions there. The Tower of Terror and Rock 'n' Roller Coaster are among her favorites. Beyond those two, there is also Toy Story Midway Mania, which is a must-do. Again, depending upon his tastes, he might also enjoy the
Lights, Motors, Action! Extreme Stunt Show as well as the
Indiana Jones Epic Stunt Spectacular!
At the Magic Kingdom, you'll want to hit all the mountains: Space Mountain, Splash Mountain, Big Thunder Mountain Railroad. Many boys his age also enjoy the opportunity to drive around the
Tomorrowland Speedway and take a spin with Buzz in Tomorrowland.
Do keep in mind that there are fabulous attractions for boys his age at all of the theme parks, so you won't be experiencing
everything by skipping a couple of the parks. That said, I think the heaviest concentration of attractions he'd enjoy can be found in the two theme parks I've suggested. Have fun!