My yearling bull was fairly gentle when I got him but at 22 months he is trying to get aggressive with me, is it just adolescence?

No, this could be more of a dominance issue that you've let him get away with, without you realizing it. At nearly 2 years old he's close to getting out of his adolescence stage, and growing into a more mature bull. This "aggression" is coming from the fact that you've failed to not just establish, but maintain dominance with him. You need to find a way to re-establish this dominance before things get out of hand and he hurts you. You don't necessarily need a big stick to do this (use it as a last resort), but rather to gently convince him to let you drive him. The key is to not push him too hard nor to corner him to the point he feels threatened.