No federal or Kentucky state law prohibits a mentally ill person from being a landlord.
While you may suspect he is (or at least was) mentally ill, unless you are a mental health professional like a psychiatrist you really can't say that with any certainty. He might not be mentally ill at all and instead simply an unpleasant person. For that reason I suggest you be careful not to tell others statements that indicate this man is in fact mentally ill or you may find yourself being sued for defamation.
It's been years since you lived there and there is nothing you can do about this guy now. He's in your past and should stay that way. Forget about him and instead focus on your future. You'll ultimately be happier doing that than continuing to let this guy bother you and bring you down.

