What to do with teens

I have a teenage son who is 15. Sometimes I despair of him EVER getting an education. He doesn’t know what he wants to do, or study, except play RPG’s for the rest of his life. I’m not sure what this is from….the 4 years he was in public school, or just his┬átemperament. His older sibs were always engrossed in something: the oldest was machine-mad….he would spend his days taking apart and fixing anything with wheels. His sister read practically every book we owned by age 15 (and we owned thousands) and his other older brother was raising saturnid caterpillars and building his own greenhouse during his early teen years. so to have this child, whose idea of a great time is to watch Heroes on TV, walk about the house aimlessly, is very disconcerting. I do feel he needs a basic education, so I insist on SOME schoolwork, like math, science, and the like. And he’s not dumb- he’s very bright. But he has, what seems to me, absolutely NO ambition. He’s good-natured and all. If I give him a job to do, he does it. He cooks dinner once a week, helps shovel snow off the roof, keeps the fire going. But then he does totally asinine things like a 3 or 4 year old in the next breath. I wouldn’t trust him in a car….he’s just not ready for his learner’s permit. (He doesn’t even want one- says it will be too expensive for driver’s ed and car insurance) What he really cares about is ACTING and theater. He is a clown, a comedian. He can do impressions so well, it’s uncanny. He spends hours watching comedians work. Hey, I like to laugh too, but he picks the most inconvenient times to display his routines. I thought, having lived through 3 teenagers and surviving them, that I had a good handle on what teenage boys are like, but this one has thrown me for a loop.