One problem with cats is that they can’t tell you when something’s bothering them. If your cat has arthritis, it could be painful for your cat, but you might have no way fo knowing except by watching how your cat’s behavior might change.
Watch how your cat holds itself to see if it uses its paws differently. If so, that could be a sign of arthritis. If your cat suddenly acts mean, that could be another sign that your cat is sick or just acting normal and bossing your around.