I know that you don't want to go to the vet. But I would take your senior cat in to make sure he isn't suffering from gum disease and an ear infection or ear mites. Both can cause alot of pain and discomfort.

He should be able to eat a good quality soft canned food or a good quality soaked dry. But if his gums are in pain he might refuse food and you would risk him losing weight. Senior animals often have a hard time regaining weight once lost...so keep an eye on him. He should also be checked for diabetes and thyroid problems.