He doesn't kill her in the end, so he doesn't hate old women. This movie reminded me a lot of my (paternal) Grandma. She had mental illness issues, a sometimes mean personality and then got dementia.
It was awful when we cared for her. It was her house, but she has scared a way a lot of people. Some old people are abusive like Owen's mother. My Grandma's doctors told us. Honestly it took a large chunk of my childhood away. I've moved passed it, but it will always be with me. I believe he made this movie for that kind of scenario.