Watching them? He's been in a coma for almost the entire arc sans a couple of plot devices here and there.I don't think that's it at all. This entire arc, Kevin's been watching his friends, mentor, and past forms of other Choujin do so much because of him, so now that his body's restored, he wants to use his own strength again after so long.
Kevin us just being his normal self: aka I HATE MY DADDY POUT.