I guess I'd be all psyched to show him his future, give him the rundown on everything that's happened from his age onward, then take a dramatic pause expecting his bewilderment only to get something like "OMG, so you're telling me that you're like all grown up and you're not even in the NBA yet? What are you, like an inch taller than me at most? LOL, you can't even dunk yet, I'm like months away from dunking..."
At which point he'd realize that I AM him, lock himself in a room and cry over his Allen Iverson posters. After a week or so he'd get it together, and get more excited about his future self
"Wow, I'll actually grow a goatee! Oh, I can't wait... Can I touch it?"
"Hey, when did you start playing bass? And an electric guitar?! OMG, play Linkin Park songs for me!!!"
"Hey, you got game, big me! Granted, don't get too cocky, I mean, no one can call himself a basketball player until he can dunk, but you're ok. Show me that double crossover again! Then buy me ice-cream!"
"Damn, your girl is hot! You hittin that?"
"Not that it's any of your business, you nosy brat, but yeah, I am "hittin" that. Btw, I'm really sorry it won't workout with that girl/crush/whatever of yours."
"Screw her, man, just promise me you'll marry this one..."
"Wait a second, is that... AN XBOX 360?!!"
Last words he'd ever say. That video game-blinded bastard wouldn't ever get back to the past. I wonder what that paradox would do to the world, though...