We've had our gelding since he was weaned. We unintentionally "spoiled him rotten" we spent a lot of time on sacking him out, to the point were I swear you could set off a bomb and he'd stand there. That being said we didn't spend time making him understand we are the boss and he is the horse. He has never kicked out but he'll nip at you and had no respect for your space, and you couldn't get him to back off even with popping him with a lead. I went back and did round pen work with him, Clinton Anderson's lounging for respect is amazing...you may try watching some of his videos..we get them on our sat. Tv :) I dvr them.
good luck, and be careful. If you feel you are in over your head make sure you get outside help.