Our 20-year-old has CKD and we feed him a prescription food in the morning (Royal Canin Renal Support D) and a non-prescription food in the evening (Forza10 Renal Support paté).
Treats are limited to catnip, cat grass, and the very rare small piece of plain chicken.
What do you feed yours?
Have you tried warming the wet food a little bit to increase the scent? Worked for mine when she was a little grumpy before she got new better anti-arthritis medication.