I agree that daily water changes are a good idea. If he is bloated thereis a good chance he is constipated. Is he still eating? Some common ways to deal with constipation are to feed shelled peas, but my fish never seem to want to eat them, especially after they are already constipated. So instead adding 1 tsp of epsom salts will usually do the trick and not hurt your fish in anyway.
But as was mentioned sometimes age does catch up, though I have usually found that they get skinny as they approach the great beyond, noramlly due to lack of eating.