A factor not considered in the discussion above is the size of the family. Back in the day families tended to be larger such that care of the oldies could be shared or one (often an unmarried daughter) could do the caring, with support, both practical and financial from her siblings.
Times have changed, families are smaller and many more live on into very old age. When we were in our 50's we had a long period when 'only child' DH's Mother, F, and maiden Aunt were all ill and need care, while my DM and her maiden sister were also ill and in and out of hospital. I had one sister but she, like me, was working full time and supporting children through tertiary education. We were in an impossible situation, and with no spare money to throw at the problem had to battle with SW and health care providers, while spending every hour of spare time, shopping, cooking, sorting finances, cleaning, hospital visiting, etc. to fill the gaps in provision.
It was always my intention to shield my DDs from the burden of caring for us, their parents, but since my DH succumbed to dementia, the truth is that I could not cope without the support of my DDs. They have also made it plain that they WANT to help their Dad in any way they can, even pointing out to me that they are blood relatives, while I am not 