I am very surprised to see so many women in their late sixties wearing flip flops this summer. Obviously a lot of older women are not embarrassed to have their feet on display.
Reading discussions about the pros and cons of the shoes-off policy you would be forgiven for thinking that a large proportion of the population cannot cope without constant ankle and arch support. At least in the UK, that impression would seem to be a mistake. A lot of older women seem to get by with minimal ankle and arch support.
I dare say that health professionals might not necessarily recommend women in their late sixties to wear flip flops, but they made the choice to wear them, so they can't be very uncomfortable.
It might be that concerns about the need for ankle and arch support are more reflective of an American context. As I understand it, podiatrists in the USA tend to discourage going shoeless, while podiatrists in the UK often recommend going barefoot indoors.