Even though the aging process is impossible to stop, it can be slowed by good nutrition, daily exercise and prompt attention to medical problems. Your cat will probably be anxious about his deteriorating abilities, especially because they were so sharp to begin with. If he was rambunctious, a decline in his agility is likely to cause stress.
Most cats tend to slow down as they age, and engage in play less often and less energetically.
But don't leave your cat to sit in some warm, cozy spot just because he is old. He needs moderate play and activity to keep his muscle tone, help prevent obesity and get his blood flowing. A stubborn reluctance to exercise may be due to stiff muscles or arthritic joints. If so, jumping and climbing may be out. Some creaky seniors find it impossible even to jump up to a favorite chair.