Perhaps he just isn't an arena work type horse? I have no solution really, as I'm young and fairly inexperienced myself, and don't know if that is "fixable" but I've heard of many horses who just get bored silly in arenas and start making trouble. Maybe he's one of those guys.
Either way I don't think OP's age should have anything to do with the replies given that it really doesn't matter when it comes to skill level. I can ride and train circles around many adult riders whom I have met, and I've met 13,14,15 year olds who can ride circles around me. It really just depends on the training you've had and your aptitude for handling certain horses.