Vet says he is really in pretty good condition for a 17 yr old but has given me 4 urine testing strips to check for diabetes. He actually seemed to enjoy being taken to the vet and getting lots of attention. Since I got the strips he has decided he is going to pee outdoors now, wouldn't you know it..
Kimmy, our cat, is nearly 20. She started drinking a lot of water & also started to go a bit despondent, so we took her to the vets & she was diagnosed with diabetes... Cost a bit to sort, but with an insulin injection in the scruff of her neck twice a day with wet pouch meals (low carb) she's fine.
For the stiff joints, we add Joint Aid for Cats (you can by it off the internet) to her breakfast (one small scoop), which has increased her suppleness.