Your father may be retired but he's not yet braindead. He is a person, he has needs, friends, interests and he moves in a different circles to you. It would be in your interest to tap this information - find out what the pain points in his circles are and develop products for those. As a rule of thumb older people tend to spend a lot of time and money on procuring chronic medication. There are many other opportunities which you may not be aware of, but your father may be aware of. Try that first...