We roughly know the recent history of longevity science, starting in the 1990s in a period in which the small scientific community interested in aging was defensive and self-policing, uninterested in any talk of treating aging as a medical condition. Young researchers were discouraged from thinking about intervention in the mechanisms of aging, or any hope of lengthening healthy human life span. Pushing that sort of viewpoint openly was career suicide. Established researchers in the field saw themselves as under siege by a tidal wave of pervasive and damaging nonsense generated by the anti-aging community of pills, potions, and outright lies, harming the prospects for building publicly funded research institutions to tackle specific age-related conditions, such as Alzheimer's disease.
Then came the work showing that single gene mutations could lengthen life in short-lived species. A rediscovery of the plasticity of longevity in response to environmental stress in worms, flies, and mice progressed from there onward. In particular there was ever greater interest and funding for calorie restriction research, mining the biochemistry of the mammalian response to low calorie intake, a part of the field put away and largely lost since the 1930s. Then the SENS rejuvenation research movement emerged just after 2000, and the thaw of a frozen research community started in earnest. Nothing proceeds rapidly in the sciences, even cultural change, and it was the late 2000s by the time that younger researchers could comfortably talk in public and publish papers about treating aging as a medical condition without career consequences. Nonetheless, that came to pass, and matters sped forward from there. Today, senolytic therapies capable of clearing senescent cells, one of the causes of aging, are under commercial development, and there is considerable excitement in the research community for this mode of intervention in the aging process. The thaw has completed, and the research community now confidently holds its own, unafraid of the anti-aging marketplace - which is just as full of nonsense and lies as it was thirty years ago.
What happened between the 1930s and the 1990s, however? Why was calorie restriction research abandoned? How did the understanding of aging progress over the 20th century? Looking back at history, we see so much of the past interest in aging and longevity as brief flashes, a few individuals undertaking it as a part of their broader research interests. Little in the way of a coherent whole emerges until our time; it is a collection of individuals, not a community. It is hard to understand the culture of the time from these few points of reference, the degree to which intervention in aging was or was not on the table as a point of interest for any particular group. Even the science fiction of the mid-20th century, usually illuminating as to the edges of scientific consideration, is unhelpful on this topic. The only assembled historical resource that I know of is Ilia Stambler's "A History of Life-Extensionism In The Twentieth Century", which actually provides much more information on a number of individuals who were at their peak of interest on the topic of aging in the late 1800s, versus what was going on between 1930 and 1950.
We can look back at a series of individual inquiries into aging across the span of very rapid technological progress in the decades to either side of 1900, leading up to, for example, the studies showing calorie restriction to slow aging and prolong healthy life in rats carried out in the 1930s. It all seems a logical progression of understanding and growth, leading somewhere. Yet after this, within the scientific community, it appears that the study of aging became ever more disconnected from practical thoughts of extending life. The closer researchers came to understanding the causes of aging, the more distanced they were from considering intervention in any organized way - the field turned to the treatment of age-related conditions, drawing an entirely artificial dividing line between aging and disease. I have no grasp on why this came to pass, at least in the first decades following the 1930s; after that, however, it is possible to draw connections and conclusions.
With the exception of the early establishment of amyloid aggregation by Alois Alzheimer, the causes of aging outlined in the SENS rejuvenation research proposals were all discovered, and those discoveries refined, in the thirty years between 1955 and 1985. The period between the 1960s and 1990s also encompasses the growth and success of the anti-aging marketplace outside the scientific community, probably spurred by the early scientific discoveries, but taking on a life of its own as people realized just how much profit could be made in this modern and more sophisticated incarnation of the old hoaxes regarding elixirs of life. For every group that approached anti-aging seriously, another ten were cheerfully selling nostrums and misrepresenting scientific discoveries - a trend that continues today.
Life extension was one of the tenets of the 1960s and 1970s culture propagated by people such as Timothy Leary, who wrote optimistically about scientific methods to dramatically extend human life span. There are probably people in the audience old enough and Californian enough to recall SMI2LE - Space Migration, Intelligence Increase, and Life Extension. The Age of Aquarius had its technological counterpart - now an overly optimistic retrofuture, only portions of which were attainable in the time span envisaged. But this movement was in no way a part of the small scientific community that studied aging, and the members of that research community rejected all of it, baby along with bathwater.
Thus to a very crude approximation, aging research in the latter half of the 20th century looks to have been steered by competing dynamics of commercially co-opted popular enthusiasm versus ivory tower rejection of that enthusiasm as a threat. There were never large numbers of thought leaders involved on either side, and the sums of money involved were never truly enormous, but this all happened in a period of growth and foundation and potential on either side of the fence. Could it have been different, and come to a better outcome for longevity science? Were those decades lost in terms of progress that could have occurred towards working healthy life extension technologies?
Everything boils down to economics in the end. It is reasonable to consider that progress only picked up in the frozen scientific community of the early 1990s because biotechnology had improved rapidly following the start of the computing revolution. Falling costs and greater capacity to generate results per unit expenditure mean fewer people must be asked for permission to perform any particular study. More exploration takes place by those with heretical views and useful curiosity. Nonetheless, we can imagine a very different world, one in which the institutional space race of the 1950s and on was instead a focus on biotechnology and aging. How much further might we be today, given massive investment on that front? It is hard to say. Could something like the Human Genome Project, for example, have been conducted at any price in the 1970s? Or any analogous feat of understanding? Drug discovery and cellular assessment were painfully slow and expensive processes back then; would it have been possible to uncover senolytic pharmaceuticals with any reliability?
But that is the root of any answer to the question of the degree to which the latter half of the 20th century was a series of lost decades in the matter of aging. We know that the scientific community retreated from engagement with the goal of extending human life, leaving that to the anti-aging marketplace, a community that did little of any great use for human longevity considering all of the effort expended, and generated much in the way of fraud, lies, and mistaken expectations along the way. A generation passed before the opportunity arose to change that state of affairs, but it is quite possible that the practical outcome might not have been all that different had it happened otherwise.