Get some body to check his teeth just in case. Buttt a flash noseband may help. I use one on my horse because he likes to run with his mouth open and gulp air and then he has to gasp for breath. It should keep his mouth close =]
Hmmm...he doesn't pay attention to you and chews on the bit. If his teeth are ok and the bit is in the proper place, I would say he needs lunged to get the excitement out of him. Let him play on the lunge line.
Another thing my trainer does with some young horses is put a rubber bit in his mouth and let him chew on it for awhile. Then when you ride him, his mouth will be tired of chewing.