The outside of his feet wear faster because he is bow legged and that is how he has to move. He lands on the outside of the hoof and then it turns a little as he walks over it. You can't change it.. tho you could slow it down with shoes.
However, if you do not ride that often, shoes and not wearing naturally will have a better chance of making him lame higher up.
Trim him level and know what you have. Post more photos when he has shed his winter coat and looks all shine, polish and spiff! :)
There is something about the outside of a horse that is good for the inside of a man. ~Winston Churchill
) Dinosaur Horse Trainer