Looks like he's molting too.
What do you feed? I would provide him with extra protein - you can give egg, fish or meat or feed him chick starter or an all flock feed. I think I would also get some poultry vitamins and direct dose him twice a week. You can find Poultry Cell at most feed stores, that would be a good choice. 1cc per 3 pounds of weight. Check to make sure his crop is emptying overnight too.
Look him over for lice/mites. For him if you are not planning on eating him any time soon, then I would use Ivermectin Pour On for treatment of lice/mites (this will treat depluming mites too). Dose for Pour On is 0.09ml per pound of weight apply to the base of the neck on the skin (must be in contact with the skin), repeat in 14 days.
Rub some vaseline into and under the scales of his leg and feet. I would put some on his comb too.
Age may be a factor, but I would try giving him a boost, tweaking his diet and treating for parasites to see if there's improvement.
How's his poop look?
