Currently 14 and a half, but I could tell myself some stuff assuming I'm going back to when I turned fourteen. Fourteen lessons, coincidentally.
First off, don't watch that porn video, you do not want that stuff in your life.
Second, high school is going to be a *****; get used to studying, don't throw it away due to videogames.
Fourth, keep your journal. Two months' worth of updating isn't fun. You won't regret archiving your life.
Fifth, stop taking shit from Kurt now instead of in 6 months. You will be a happier person.
Sixth, AP Bio requires four A's in the Chemistry courses. Call the school NOW and switch into regular Bio this year; you'll get called stupid but you won't be taking it as a sophomore like all the other people who forgot to read the course description.
Seventh, start working out now and not in 6 months. You might actually have some muscles that way.
Eighth, eat some damn fruit.
Ninth, you are going to meet a man called Greg. He is going to be one of the best friends you have, despite being twice your age and three thousand miles away. Don't quit WoW until you befriend him to the point of exchanging emails.
Tenth, quit World of Warcraft as soon as you've built up your relationship with Greg, instead of 6 months from now; you'll thank yourself for it. Don't get hooked like your future self did.
Eleventh, do your fucking homework. Grades are the most important thing in the world for the next four years and you can't afford to miss an A by two points that were lost because you were too lazy to do your damn homework.
Twelfth, don't take APCS. You're going to suck at it, better to take Intro. You'll stay in English period 6 and you won't have to take all that shit from Spencer, Hunter, and Brad.
Thirteenth, don't think with what little dick you have. Girls don't matter. Brains matter. Don't slack.
Fourteenth and final, for most of the rest of your life, or at least as far as I know, you are going to sleep poorly. Train yourself to deal with it during the rest of the summer and you won't miss crucial points in Geometry class.
I would then shake my hand, kick my balls, salute myself and go back.