I don't get that impression from my (limited) knowledge of the field. If Stipp's book is accurate then there have been many attempts in the last hundred years by serious scientists.

Then you should re-read that book -- it was espousing exactly my own position in this dialogue!

1. I never said nobody before had ever tried to do anything that would potentially impact human longevity scientifically.

2. I did say that antiagapics research as a primary goal has never before this generation existed within the mainstream medical community.

3. Point #2 was the entire purpose of the book you're trying to cite as a contradiction of my position.

4. The overwhelming majority of work done previously was either not directly intended to the effect of preventing aging in humans or else was done by 'fringe' actors without generalized support from the general consensus as to their topics being worthwhile endeavors before their results came in. (I add this qualifier to make it clear I'm not talking about after-the-fact 'well, clearly that was foolish. It didn't work' stuff.)

This can't be all that matters if the same result would not have occurred in 1950 or 1900 (or even more to the point 1850). That means that at least one premise needs to be not just about topical focus but about the overarching technological level

This is asinine. Science is a convergent, not a divergent, endeavor. Increased knowledge in one field necessarily alters or amplifies the impact of knowledge in another. I said nothing to contradict this and gave several examples of it being affirmed.

Regarding your predictionbook listings: I put a very low probability of resveratrol hitting the public market within twenty years, but only because I am familiar with the FDA approvals process and how convoluted it is. I'd estimate more like in the 20's-40's for the 2025 date, and I do not believe it to be possible at this point for the 2019 date. I don't find your estimate of the millennarian proposal exceptional.

It could turn out that humans already do something to their cells that mimics most of the effects of reservatrol.

This is a testable hypothesis and it has already been falsified. We share cellular metabolism with calorie unrestricted organisms, and not with CR-organisms. Furthermore, while human lifespans are longer than most mammals (not all but most), they certainly aren't by any means exceptional for even warm-blooded organisms in general.

Moreover, one can easily conceive of circumstances where many of the proposed anti-aging systems just won't work

Sure. But that's irrelevant. With the topic having received, finally, mainstream attention -- we've gone from the periodic instance of the isolated potential investigation to the spaghetti method: throw everything at the wall and see what sticks.

That being said:

[The claim that within fifty years from today, antiagapics research will have extended human lifespans by at least another fifty years] is in context a bit stronger than this because you seem to be claiming not that people born fifty years from now will have a lifespan extension of another fifty years but that this will apply to people who are already old.

Nowhere did I ever make that claim. The closest you might come to this is the fact that I was applying it to people my own age. I am currently thirty. If resveratrol is approved by the time I am fifty (i.e.; 2031), then my taking it at that point will (assuming resveratrol extends remaining life expectancy by 50%), will extend what would otherwise be roughly 30 years to 45 years. Should tissue-cloning further provide genetically-identical-but-metabolically-barely-post-adolescent organs, then I should expect that this would provide heightened vitality to extend at least another ten to fifteen years of life. Etc., etc..

If this problem is severe enough, it is possible that there are diseases which will show up in the very elderly that we haven't even noticed yet because the population of such people is just too small.

That's a common field of topic for geriatrics-study in general. Topically reproductive fitness tends to drop to zero sometime before the age of sixty in humans. Yet, when health impediments and nutrition are eliminated as problems (1st-world-countries), women still tend to live a few years longer than men. Most conjecture on this has it that women are 'more useful' than men evolutionarily even at older ages: grandmas can care for the little 'uns which lets mom make the food. Etc., etc..

A lot of the behavioral trends, patterns, and complications associated with senescence in humans are very well understood: that is, after all, the entire focus of geriontology.