Disclaimer: I strongly support anti-aging research. It's obviously a great idea. And, like a lot of other cryonicists, I think that longevity escape velocity is unlikely to come about anytime soon and that cryonics is much more likely to work for me, my loved ones, and other people alive today.
Context: A recent LW post suggested that pursuing anti-aging was more feasible than cryonics (as somewhat of an aside of an interesting, in-depth article about anti-aging interventions). It was cross-posted on Reddit here. u/Calm-Meet9916 had a great response based on reference class forecasting, known on LW as the "Outside View", that I wanted to signal-boost here because I think it is important to present the counter case about the relative feasibility of cryonics vs LEV.
Quote from First Comment: "There is no basis for claiming that anti-aging is more feasible than cryonics or more feasible than cryonics for people under 50. Looking at the last 20-30 years, predictions for anti-aging were that we'll have robust mouse rejuvenation by now. We don't and we aren't even close. The little progress that has been made has not been translated to humans and there is no reason to believe that it will (as with dementia and Alzheimers disease which has consistently failed over the last 30+ years). By the time anything of significance gets translated to humans, people who are today under 50 will be in quite bad shape."
Quote from Second Comment: "In his first TED talk in 2005 Aubrey's message was that we have 90% chance for robust mouse rejuvenation in 10 years if $100 million per year would be invested philanthropically. We're now in 2021, 16 years from his talk, funding overall is much greater than $100 million per year, although it's not just philanthropic. And what are the results? We can increase mouse lifespan on average by 25% with senolytics. That's it. We're very far from RMR and I'd say that his prediction (or his message, or whatever you want to call it) has been overoptimistic by at least 3-4 decades, possibly more.
On one hand I understand that it's hard to get public excited by saying "you will not benefit, two generations from now will", but on the other, it's detrimental to cryonics if people think "we'll have human rejuvenation in 20 years, don't bother". It prevents people from considering cryonics, as is the case right now for the vast majority of anti-aging movement. Of course there are other reasons people don't like cryonics, but still, promises of rejuvenation is one of them.
It's funny that you mention [Joao Pedro de] Magalhaes, since he publicly said many times that he doesn't expect any significant life extension in his lifetime. I don't know if any of other researchers that you mentioned has been public about timelines, I know that Judith Campisi and Nir Barzilai always distance themselves from any claims about near term results and prefer to talk about benefits for next generation.
But whatever the case may be, we shouldn't argue by delegating to authority. Consider what was the actual progress in the last 20-30 years. To my knowledge, solid cancers (which represent the vast majority of cancers) are still incurable, cardiovascular disease still causes one third of all deaths, dementia/Alzheimer's is basically where it was 30 years ago (incurable), we don't know how to break down glucosepane (or other advanced glycation endproducts), we don't know how to treat presbyopia (hardening of eye lens causing vision loss), etc. Basically we don't have any significant results in any category. There is no evidence of it (research is not evidence, research is just research).
That doesn't mean that nothing happened in the last 20 years, but that rate of progress is not as fast as people excited about the vision think it is. Biological experiments take time, they refuse to go faster, and there's no way around them."
My Comment: To add one more reference class data point suggesting that progress against aging will take a long time, consider that many anti-aging researchers in the first half of the 20th century thought that aging could be usefully tackled using the research tools of their era. According to Ilia Stambler, a typical anti-aging researcher thought that a short-term goal would be a lifespan of approximately 100 year lifespans and a long-term goal would be 150-200 year lifespans [citation: A History of Life-extensionism in the Twentieth Century, page 50]. But in hindsight, we can see that they were mistaken, at least if we consider the past 70-120 years to constitute the "short term," as we have not yet reached 100 year median lifespans and seem nowhere close to 150-200 year lifespans. (Gompertz would like a word about that as well.)
My personal guess is that most major gains against aging will come once we have a much better understanding of basic biology and that this will be gained primarily by building largely unsupervised computer models. This may be possible within the next couple of decades. (Of course, there are risks to the development of such computer models.)
But what of the reference class forecasts of cryonics? Arguably the early storage failures from 1967-1980 are a data point against very early optimism, such as that of Cooper and Ettinger. But since the bitter lessons learned then, the rate of storage failure has gone way down. And the argument that the people still stored may one day be able to be revived does not seem weaker today than it did earlier. If anything, it seems more likely, as progress towards whole brain emulation or molecular nanotechnology inch forward.