Randi, as far as I know feeding an older cat a high protein diet shouldn't hurt them unless they have kidney disease. Also feeding a cat a high protein diet won't cause kidney disease. This is what I've read. My Storm is 15 and he's been eating a high protein diet for several years now. All of my cats are now on Wellness Core dry food which is 50% protein. My 4 oldest cats are also eating the Wellness grain free canned food which is 10% protein and they all love the 5 flavors that it comes in: Turkey, Turkey & Salmon, Chicken, Chicken & Herring, and Chicken & Beef. I would also feed the canned food to Alani & Blaze but they still have very sensitive tummies and so it causes them to make loose stools. I hope that whatever you decide to buy for Fister that he'll approve. Good luck.