Humor of Japanese elderly women? Are you asking what Japanese elderly women laugh at? Or are you asking what their humorous behaviors are?
I don't think your categorization of "Japanese elderly women" makes sense for "humor". I mean categorization of "humor" depends rather on their living area, life style or their education.
Example joke 1:
Yesterday, my grandfather bought a book "How to prevent senility".
Today, he bought the same book again.
Example joke 2:
When I was in the personal closet in the airport, a man in next closet talked to me. "Hi! are you fine?"
I replied "mm, eh.. so so...".
He continued "well .... then .... what are you doing right now?".
though I feel strange, I replied stupidly "Now I'm going to put something out just like as you!".
Then he started whispering "I will call you back later on.... some idiot in next closet replies to me...".
Example performance:
I think people of wide range of ages will enjoy these jokes.