Well it sounds like alzheimers but it could also be dementia. Dementia is suspected when there is impairment of two or more brain functions, including language, memory, visual-spatial perception, emotional behavior or personality, and cognitive skills (such as calculation, abstraction, or judgment).
It can be caused by aging,impairment of the vascular or neurologic structures of the brain. Most is caused by hardening of the arteries.
Certain medications that elderly people take may make him behave this way also.
He should be evaluated by a doctor as he may have some very helpful treatments, depending on the cause.
Good luck trying to help him. You are a kind person.