Even bad-tempered old humans usually have a reason for it! Is his own food biscuits and your leftovers softer? Have you had his teeth checked recently? Are his anal glands all right, or is it painful to do his business in the garden because they are infected (very common in Cavaliers)? Enjoying walks is normal Cavalier behaviour - even when they are ill or in pain, walks enable dogs to switch off from what troubles them, so enjoying walks doesn't mean that they can't also have an underlying physical problem. Being grumpy is very untypical of even the oldest Cavaliers and almost always does mean pain somewhere. It may only be a bit of arthritis that gives Charlie a twinge when he has to get up to go out in the garden, or a bad tooth that would be helped by having different food (one of mine stopped eating and just needed a smaller size biscuit because his teeth were bad) - something quite simple that a visit to the vet will be able to help, rather than just dismiss Charlie as a miserable old git!

Kate and Ruby (who can be growly - but then she is a rescue with syringomyelia, so I reckon she's got reason to be!)