"I had to retire before

I could contemplate it," someone has just told me.
She has in fact just taken on a new job as President of an international organisation. I belong to the same organisation so I have some idea of the enormity of the task she has just taken on. She starts in October and I hope she has a holiday before then because she is not going to get one for the next two years. 
Yes, it is "one of those jobs". It is the sort of job you can only do properly if you don't have another job but it is not one you are going to get paid for doing. 
It is also a job which needs to be done and which you need to be committed to doing. It means travelling and a great many meetings and an international conference and... well, I am sure you have the general idea. 
Some of it might be fun I suppose but there will be very little of that compared with the amount of work involved. It is going to take commitment - of which I don't doubt she has plenty. 
Her appointment has left me contemplating something yet again. How are some of these roles going to be filled when people are working longer?
The "retirement" age is creeping ever upwards. We are told this is essential as people live longer and society can no longer afford to support increasing numbers of "old" people. But some "old" people still work. My paternal grandfather was 86 when he "retired" - and he only ceased to work when his eyesight failed. My maternal grandfather died at 68 - while he was still working. The Senior Cat "retired" from teaching and promptly took up another role and then another. He is still doing some teaching at 92. 
If I am intellectually capable I will work well beyond retirement age. My job is not a physical one.
And that, of course, is the issue in the minds of people. Those people who don't do physical work can, if they are intellectually able and have the necessary skills and training, work longer. Those who do physical work may not be able to work as long. It's a problem which gets discussed but, so far, it has not been given really serious consideration. 
But there is the other issue. If people retire later, who is going to take on the role of president of an organisation like the one I mentioned at the start? If the new president had to wait another five years I doubt she would want to take on the role. Five years can see big physical changes at that age.
Who is going to take on all the other "voluntary" work which is now done mostly by older people? Will they still be expected to do all this and care for the grandchildren? Is  "retirement" going to be a thing of the past for many people? 
Does there come a point where people should not be expected to work unless they choose to do so - or should we just continue to work until we can no longer do so?