Q. My 10 year old mix constantly licks and chews on him self
A. Usually licking and chewing (itchy) is a sign of allergies. They can be environmental or from food.
It would be good to discuss with your vet as they may have some medication to help make him more comfortable they can prescribe.
I also recommend putting him on a grain feed food of good quality and change the type of protein to something different than what he has been eating. This should help if it was a good allergy. Environmental allergies can be more difficult to diagnose. But tests can be performed.