I totally hear you. My solution to this problem was to let my boys write about things they knew a lot about, or had an opinion about, but weren’t very academic. They wrote about which dirt bike we have is the better one, why birds are a better pet than dogs, the process of building a certain thing out of Lego, a description of a snow fort they built, etc. The topic doesn’t matter, in my opinion. What matters is the process of writing. The topics will mature as they mature. Honestly, sometimes I think writing curriculum expects too much of teenagers. Sometimes they just don’t care about those topics! So find a topic that interests him. I would even let him write about his sister staying out of his room, as long as his writing is well-organized and done properly. 🙂