Any type of disease that can afflict humans can also affect cats. As cats (and humans) age, they can lose their hearing. Then again, it’s hard to tell when a cat’s just ignoring you and when it can’t hear any more.
Cats can lose their hearing from illness or if their ear drum gets ruptured. If a cat starts meowing louder than normal, it could be a sign that its hearing is going. Or it could be a sign that your cat just wants to boss you around louder than before.