I never like to say something is due just to old age unless we prove otherwise. I would worry that the symptoms you describe could indicate there is something else going on. I don't know if lab work was done but things like a low potassium or red blood cell count could cause the weakness, along with kidney disease or if his thyroid is not controlled. Another treatable condition many older cats can have is high blood pressure. I would suggest you take him back to your veterinarian to find out the underlying cause of his symptoms. It is true that there are some things in an older cat that we cannot cure, but in most cases we can at least make the cat more comfortable. As far as his eating, when his appetite is down the best you can do is making a little kitty buffet and offer him various things. You can try to warm some of the food in the microwave to increase its smell. There are appetite stimulants we can use in cats as well so be sure to ask your veterinarian about this.
More...
The Colonel came to me as a stray three years ago, the vet guessed his age at around 
Linear Mode
