A. Due to his age it is likely that your kitty has painful hips from arthritis and therefore does not move as much around as he used to . This makes the muscles atrophy and therefore the legs would appear mor skinny. I suggest you see a veterinarian specialised in cat medicine as they would after checking the kidney function of your cat, prescribe your kitty an NSAID such as Meloxicam (licensed for cats in Europe, licensed for dogs only in the USA, but can be prescribed off-license) to reduce inflammation and consequently reduce pain, so that he will be moving better again.
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