About the time my mother-in-law was 80, we began to be worried about her mental health.
She would lose things she had never lost before. She would tell us someone had been in her house and stolen things. And most important of all, she could not manage her medication: her inhalers (for emphysema) would be used up in a couple of days, instead of a month!
For some years, since her husband died, I had been taking her to the supermarket each week, and over that time she had lost track of her pin number for her card at the checkout.
So the writing was on the wall.