How much work does he get? Exercise, training, playing, a male boxer needs several hours attention a day. They never really grow up, just get more canny in the way they run rings round you. Try obedience, agility, cross country running.
Castration would not help him calm down in a physical sense, but would stop him getting upset if there are bitches in season, or other males near to him. It might also help with dominant aggression, but if this is learned behaviour it is more difficult to cure.