My father acts immature sometimes. He talks constantly about anything to anyone. People avoid him because of this. His grandchildren don't come over because they know they will be stuck listening to his stories for hours. I am seeing a counselor because I think I have some resentment towards my father. I don't want to disrespect my father, but I need some patience. Anyone else feel this way?
I learned to tune him out, escaped to my own little world. He wasn't going to change so I had to change my mindset.
If the test does indicate he has the beginning of decline, it will help you a lot to educate yourself on dementia. Teepa Snow has many wonderful videos on YouTube, which will help you learn how to better engage with him so that your interactions are more peaceful and productive.
There are strategies, such as redirection, when he starts repeating. Come up with another topic (and it can be completely unrelated). Just keep changing the topic. Or start an activity with him (sorting something, a puzzle, fixing something, food prep, etc). If it gets really bad you can just walk out of the room, no explanation needed. If he's mentally dysfunctional, mentally ill or has cognitive problems, then you won't be able to change the behavior (as others here have also stated). So, you are the change. If he has cognitive impairment then he cannot change his own behavior and haranguing him about it would be unproductive and cruel. For many age-related problems there are no good solutions, only least bad options.