Im 27 and I live with my mother who is 59. Without getting into dementia and serious issues. I have noticed that parents as they get older, beocme more like kids again, they need that extra special attention and care. THey know theyre getting old, theyre not what they used to be etc.
Even though I know it would be hard, I urge you to be more patient with him, yes he needs to respect your privacy as well. But I think sit and talk to him like you would a small child and explain him gently and tactfully. Make time for spending quality time with him like say Saturdays play chess or bridge or whatever, so that he looks forward to that and wont find the need to maybe barge unexpectedly.
You seem like a lovely daughter who is considerate as speakig to him loudly made you feel guilty sort of. I really respect people who take care of their elderely parents when needed. rather be patient with him, the day he is not there you will find yourself wishing you hadnt been harsh.
All the best