OP, you are being given a harsh time but not for the reasons you think.
There is an overly narrow view of when people 'should' stop work, and it sounds as though your friend has fallen foul of this. But so have workplaces as a whole.
I work with a woman in her early 70s who is an absolute joy to work with (hope that doesn't sound too patronising but she is one of the nicest people I have ever worked with). She is PA to the director of my division at work, and as an old school, properly trained secretary with decades of experience who will prove very difficult, if not impossible to replace. Ideally she should be in some kind of consultancy/training role but is v happy working part time (though still 3-4 days a week) in a role she has been in for a long time. She's sharp and fun (comes out for a couple wines with us on occasion!) and imo should be in work. Its good for us, its good for her, its good for the work place.
Similarly I had a genetics lecturer at uni who was 81! He was a gorgeous old man who winged that the uni were trying to retire him which was why he was only in one day a week. But his presence means I had lectures from a person who had been around since the dawn of genetics, and therefore was able to make a complicated subject very accessible by explaining how we got to where we are now. We used to joke about his dead sea scroll slides, he laughed and made filthy jokes. Im probably one of the last people to have been lectured by someone who had been around since the dawn of that subject and that was only made possible as he worked until he was (at least) 81.
However OP, both of these people were willing and able to do so. By knowing them I don't look at my life as a deadline extending towards the knackers yard when I retire. On the other hand, I will be lucky if I reach their ages and I am still as young in body and mind as these two were.
There needs to be a better attitude towards older workers, but also more willingness to consider work on an ability rather than needs basis. Some of it is more in the mind than actuality imo.
We need to have a serious debate about making hard, physical careers such as teaching, retail and nursing more accessible to older and disabled people with expertise to share.