I agree with Barefoot. It's a pity that this poor boy had a bad start and has associated being ridden with fear, danger & needing to defend himself. It's not his age that's the potential problem, but his first impressions that need to be overcome.
Not knowing your experience, I can only say that I would advise he is trained very gradually and positively, in a non-confrontational manner, with lots of approach & retreat. He will need someone who can read his smallest signals of stress(such as holding his breath, etc) and treat him accordingly and considerately.
I also think that he needs someone who is a good rider & not afraid of bucking. You want him trained in a way that will avoid causing this defensiveness, but if by chance something happens to frighten him, it would be a good thing if it didn't end in him ridding himself of the rider! :roll:
If you reckon you fit the bill, go for it! But otherwise, choose your professional very carefully. I'd also be inclined to watch them working with other troubled horses before I gave them the reins on this boy.