Note that this proposal is also in the context of a system that provides full support for job retraining and unemployment pay in the gaps (and a good disability and mental-health system), so if you run into serious problems you have options.
Maybe wanting to stop working at 65 and step into full retirement is particular to the American system. Most 70 year olds I know would like some kind of job/retirement hybrid: work 30 hours a week, have longer vacation times, more flexible hours, not losing the job when you have to take a leave for medical reasons, etc.
My father is almost 70, and going on hikes with him leaves me pretty winded. Certainly no walk in the park. I'm just a little more than one third of his age. If he would do some strength training in addition to his jogs and hikes, I imagine he would be in great overall shape.
I don't think that I'll necessarily be anywhere near his physical fitness when that time comes. But with retirement or a decreased workload, I intend to dedicate more time to keeping fit and treating my body as more of a temple.
With societies obsession over youth these days, it's gonna be interesting to see how the youth of today hold up in forty to fifty years.
At 70, your body is generally not able to do the same things you were doing at 20/30, at least not with the same ease. A 75 year old man could work as hard as a 25 year old man, but the same amount of work will probably take a greater toll on his health.
In a way, seems like his scheme is pretty much geared to make people dread reaching old age, and a reduction in pension payments would come from all the people committing suicide after facing the realization that as their bodies become more tired and less resilient, they will have to work harder.