I have a cocker spaniel who turned 16 last month. She had her annual checkup recently and I am very grateful that the vet says she's exceptionally healthy. But there are, of course, the physical signs of age...
She tore the ligaments in both back legs when she was about 8 and has prosthetic ligaments now. A few years ago, we noticed her falling backward when she tried to jump onto chairs, and about a year or two ago, she completely stopped trying. The vet says she has no signs of arthritis, "just a little muscle weakness back there; happens to all of us." She's a little slow now when she first gets up from lying down, and her legs crack several times.
She's lost a bit of weight...2 pounds or so, but again, vet says that's okay. Her spine does protrude more now, but she eats normally. She'll still attempt the stairs on her own; if it's dark out, she needs the light on. She has walked into a few things here and there. You can also stand right next to her and shout her name...no reaction. You have to touch her to get her attention. I also noticed; she's white with red spots, but she has a lot less red than she used to. What little she does have left has faded.
The worst is that she's developed "geriatric vestibular syndrome" in her ears. We thought she was having a stroke at first! She'll try to walk, but she'll go sideways, with her head cocked to one side, her ears perked. One of her back legs will thump up and down, like a spasm, and her rear end will drop. This will go on for about half an hour at a time, during which she can't settle down. Tires her out, that's for sure. But again, the vet said it happens, we really can't do anything about it, but it's not life-threatening.
It's hard to watch them get old...

to all!