From what I have read, hoarding is considered a form of mental illness. Also, if he's aggressive, it could indicate that some more than age related decline is involved. If he's not mentally competent, he may need real intervention by professionals to assist him, regardless of whether is is aware of it. Adult Protective Services may be able to help or you could talk with his doctor, if you have that authority.
Would you consider calling your local Area Agency on Aging and asking for a needs assessment? If his living conditions are truly unsafe, they can take action.
Does he have a doctor? While his doctor most likely cannot talk to you about his symptoms, you can report them to his doctor.
Would you consider calling your local Area Agency on Aging and asking for a needs assessment? If his living conditions are truly unsafe, they can take action.