My old girl is fourteen and a half. She sleeps on my bed a lot, and as she is deaf she doesn't always hear when its dinner time and the food bowls start clanging, so I turn the landing light on and off a couple of times and she appears as if by magic having noticed the light.
This morning she was under the bed and wouldn't come out, was a bit worried what I might find when I got home after going out for a couple of hours. She was downstairs with the others when I got home, and her nose was muddy where she had obviously been burying (or digging up) something in the garden. Ate her tea tonight as normal, then wandered off to bed for the evening. At that age, I let her do as she pleases, and if that means doing a poo where she shouldn't every now and then, well so be it.
I am sure she will let me know when the time comes to let her go.