[anonymously]

You may find some helpful information here: http://skeptvet.com/Blog/
See: “More Nonsense from Holistic Vets about Commercial Therapeutic Diets”
Posted on July 20, 2016 by skeptvet

PS: Canine environmental allergies get worse with age, consider consulting a board certified veterinary dermatologist regarding “skin problems”.
/forums/search/allergies/

Also, has he had a senior workup, labs, etc? If not, I would start there.