It's sad when they lose their marbles.
Had one a couple of years ago. Probably mid-90's age wise and she started getting "dithery" and taking time to "find" her money.
Then one day I turn up and knock the door and she looks at me and says "Who are you?" I say "I'm your window cleaner Mrs. H." (been calling over 10 years) She replies "Oh yes." And I clean and she pays me.
Finally I called and she said "You look just like my window cleaner!" I said "I am your window cleaner."
She said "No, you're not, my window cleaner is called Malcolm."
Me: "Yes that's me! I'm Malcolm, the window cleaner."
Her: "Yes I know, he's my window cleaner, not you."
And she shut the door.
A few months later a chap came out (her son - sorting out the estate) and told me she had gone into a home and died.
Sad. Lovely lady.