My Dad got weird too when he got much older. He got quite snappy and picked on me a lot about very insignificant things. It was strange. He didn't do that to my sister. And he always was loving before. He was depressed, I'm sure and kind of withdrew. He didn't have any kind of meaningful conversation with me...very little conversation at all during about the last 10 years he was around. My Mom is turning 90 in about two weeks and she isn't grumpy at all. So, maybe old age combined with something in someone's personality just produces this atypical behavior from them. It's sad really. But at the same time, very difficult for those around them.
It is good that Hannah doesn't have to put up with that too often at least.