I know this is a snake forum, and I probably won't get very many answers, but I just need to know how long until he needs to be put to sleep..

Today when I was picked up after school my dad had told me that my (second oldest) sister had told him earlier that our dog, Max (13 y/o German shepard/Australian shepard mix, turning 14 y/o in January), could not get up off of the floor. So, I'm guessing his legs gave out because when dogs get old their tail bones get bad and the dog would have a hard time walking around, sitting, getting up, etc. I've had this dog ever since I was 1, and I'm only 2 months older than him, so it's really hard for me to lose this dog. How long do you think he'd probably last until he has to get put down?