Some opponents of increased human healthy longevity argue that if we begin to live for far longer than the present human life span then progress in technology will slow to a crawl. This is often presented as a variation on the stagnation argument: that long-lived people will cling to their ideas and their positions for decades or centuries, resisting all change. It is true that human nature comes with a strong conservative streak, and all change is opposed. But despite that fact change nonetheless happens on a timescale quite short in comparison to human life spans: leaders come and go, like fashions, and revolutions, and changes of opinion, and sweeping redefinitions in culture and society. Rare indeed are those that manage to last for a couple of decades, never mind longer. This pace of change in human affairs is essentially the same as that of the ancient world, despite our much greater adult life expectancy in comparison to the classical Greek period or Roman empire.
If we want to look at raw correlations on the other hand, it seems that the technologies needed to extend healthy life go hand in hand with an increased rate of technological progress. Longevity has made the human world become wealthier and run faster, opening doors of opportunity rather than closing them. The only way to increase the healthy human life span is through the creation of a broad pyramid of enabling technologies that in turn lead to faster progress in all fields, not just medicine. Computing is the present dominant enabler, for example, not just for biotechnology but also for almost all other fields of endeavor. If human nature to date has failed to hold back the tide of progress, I'd say it has little chance at doing so in the future: progress is only speeding up.
As is pointed out in the article excerpted below, people change throughout their lives. This also is the same as in the times of antiquity, despite much longer life spans. Human nature is human nature, and the caricature of inflexible, static old people is just that: a caricature. Minds change, and where the elderly are in fact forced into smaller and smaller circles it is largely through disability and frailty, not choice: the failing body and mind narrow the accessible vista, not the lack of will.
We are all still children. As far as the Centenarian is concerned, the only people to have ever lived have been children - and we have all died before our coming of age. What if humans only lived to age 20? Consider how much less it would be possible to know, to experience, and to do. Most people would agree that a maximum lifespan of 20 years is extremely circumcising and limiting - a travesty. However, it is only because we ourselves have lived past such an age that we feel intuitively as though a maximum lifespan of 20 years would be a worse state of affairs than a maximum lifespan of 100. And it is only because we ourselves have not lived past the age of 100 that we fail to have similar feelings regarding death at the age of 100. This doesn't seem like such a tragedy to us - but it is a tragedy, and arguably one as extensive as death at age 20.
The current breadth and depth of the world and its past are far too gargantuan to be encompassed by a mere 100 years. If you really think that there are only so many things that can be done in a lifetime, you simply haven't lived long enough or broadly enough. There is more to the wide whorl of the world than the confines and extents of our own particular cultural narrative and native milieu.
Luckily, functional decline as a correlate of age is on the way out. We will live to 100 not in a period of decline upon hitting our mid-twenties, but in a continuing period of youthfulness. There are no longevity therapies on the table that offer to truly prolong life indefinitely without actually reversing aging. Thus, one of the impediments preventing us from seeing death at 100 as a tragedy, as dying before one's time, will be put to rest as well. When we see a 100 year old die in future, they will have the young face of someone who we feel today has died before their time. We won't be intuitively inclined to look back upon the gradual loss of function and physiological-robustness as leading to and foretelling this point, thereby making it seem inevitable or somehow natural. We will see a terribly sad 20 year old, wishing they had more time.
It seems to me a truism that we get smarter, more ethical and more deliberative as we age. To think otherwise is in many cases derivative of the notion that physiology and experience alike are on the decline once we "peak" in our mid-twenties, downhill into old age - which does undoubtedly happen, and which inarguably does cause functional decline. But longevity therapies are nothing more nor less than the maintenance of normative functionality; longevity therapies would thus not only negate the functional decline that comes with old age, [but also] the source of the problem arguably at the heart of the concern that longer life will slow progress.
Increasing longevity will not bring with it prolonged old-age, a frozen decay and decrepit delay, but will instead prolong our youthful lives and make us continually growing beings, getting smarter and more ethical all the time.
Lastly, this thought: so what if increased life spans did slow progress? Even in the hypothetical world in which that did look even remotely plausible, it is still the case that for so long as the pace of longevity is greater than the slowdown, everyone still comes out ahead. Being alive and in good health is the important thing: given that, the only thing that matters with regard to further technological progress is whether it is happening fast enough to keep you alive and in good health. Everything else in life is what you make of it.