Good weapon for the elderly
I would recommend a Glock 19 for your father. It will never jam, he will have 10 rounds, if he can handle a 45 cal the Glock 21 may be better if he is really at risk, 1 shot and they will be on their back.
This reminds me of a really funny story, I talked my wife, who hates guns, into getting her CC permit and I went to class with her to help her pass the range test, she barely made it with my Glock 19., anyway as we were entering the indoor shooting range I notice an elderly lady coming in the door with a walker, a closer look at her walker and she had a Kimber 45 cal with a custom holster as well as mag holders attached to her walker. I later watched her shoot and she was very good, I love it!! Only in Arizona.