I know "someone" who has a 17 year old cat. He is not very "sick" so to speak. But he does have an eye issue, maybe cataracts, maybe something else. He does see, how well who knows, and his hearing his fine. The vet thinks a thyroid problem but just the diagnostic tests run into hundreds of dollars never mind the actual treatment. He pukes on the carpet (the ones they actually find) about 5 times a week and sometimes they find little shit balls around the house. He also sometimes scrapes his ass on the rug after taking a dump. He constantly needs attention, he will stare at you and meow non-stop every waking minute. It is incredibly grating on the nerves listening to "meow" everywhere you go the entire day and having to watch your steps in fear of tripping over him as he is always right at your feet. The vet said he doesn't seem to have any kind of pain, just needs lots of attention. Google says the onset of senility is a common reason. The nights are tough as he gets into a meow fit once or twice a night as they attempt to sleep. The kids are out of the house so it's just Mr and Mrs 55+ year old to take care of him. And they ain't getting any younger so the patience factor is rapidly disappearing. He's been a house cat his whole life and is deathly afraid of strangers. A relocation would be too traumatic for him. Just getting him into the car to go to the vet is a nightmare as he has peed in the car on the way and gives that low meow groan the whole way. Is it an awful thought to have him put down? Is this an accepted yet untalked about practice? Ugh.