This is getting a bit messy, let's recap.

The original disagreement was you saying "The concept of retirement is ... fairly new" and me disagreeing. I still think that sentence is plainly false for most sane values of "retirement".

You also said that what's new is the idea of retiring at a particular age, in cohorts, and that's kinda true. Only kinda because first, as your Wiki link shows, that idea in its contemporary form appeared more than a hundred years ago; and second, because retiring after a term of service is an ancient custom, going back to the Romans (as usual :-D). The Roman army conscripted young men who served for 25 years after which they retired -- they were released from the military service and given a noticeable sum of money and a plot of land. That practice (conscripting young men for a long term of service with a large payout or an annuity at the end) survived in some armies until the XIX century.

I also disagree with pretty much all of this passage, I don't think it correctly reflects life in pre-industrial societies:

Only a few people lived for many years after becoming physically or mentally decrepit and unable to do productive work; most people declined and died unexpectedly and quickly. The rich and ruling classes grew ever richer and more powerful until their deaths; old kings, generals and businessmen didn't sit around "waiting for death peacefully", they kept doing the same things they had always done, just less vigorously.

Going back to the question of why contemporary retirees are... problematic, let me suggest what I think is a standard explanation -- the main cause is the breakdown of the extended family and the alienating character of cities.

Imagine someone old and frail in a village. She lives in a house (or a hut) with her family, many of them her descendants. There is a lot of life going all around her. There is an innumerable number of small tasks which she can do -- watch the grandkids, patch up some clothes, cook something for the workers, fix the hole in the wall, etc. etc. She is not isolated, she continues to be part of her family and part of her community. She always has something to do.

Compare that to an opposite case: someone old and frail living in an apartment in a big city. She lives alone because her single child has his own family and lives far away. The only things she really needs to do is shop for food, cook it (or eat out of the can), and clean the apartment. She doesn't have much of a support network -- the great majority of people she sees every day are strangers. And, of course, there is the idiot box to make the passing of time less painful...

About Luddites -- I agree that "the textile machines priced humans out of the market is a fact". The point, however, is the link between machinery and unemployment -- the link which you asserted in your original comment and what the Luddites really cared about. I doubt they were terrible attached to manual weaving -- what they wanted was a job, sustenance. Both the Luddites and you say that automation causes unemployment and that is empirically not true. Whether it continues to be not true is, of course, a different question.

As to predicting the future, yes, I have a low prior for specific predictions far into the future (50+ years) because I don't think there's any evidence that humans can consistently do that. In this particular case you're not predicting that the usual pattern will continue, but you argue that it will break, so it seems to me the burden of proof is on you to show why that pattern will not hold.