When it comes to persuading the public to support work on the development of rejuvenation therapies, it sometimes seems that, even after years of effort, we're still somewhat stuck at the point of convincing people that therapies to push back aging and extend life will result in more healthy years rather than an extended period of ever-increasing decrepitude. The knee-jerk response to the goal of life extension is to imagine an eking out of the period of pain, suffering, and ill-health at the end of life. Obviously, this isn't all that attractive a prospect. Yet it was never the goal: therapies that successfully treat the causes of aging, repairing the accumulated cell and tissue damage that lies at the root of aging, will produce rejuvenation and additional healthy years. Despite a couple of decades of messaging from the scientific community and advocates for healthy life extension, all telling the public that extended health and youth is the goal, we still run headlong into this false expectation of an extended old age of sickness and diminishment.
Whenever the topic of increasing human lifespan is discussed the concern is sometimes raised that a longer life would mean a life spent frail and decrepit. This is sometimes known as the Tithonus error and shows a fundamental misunderstanding of the aims of rejuvenation biotechnology. Tithonus, as the story goes, was granted immortality by Zeus, but the father of the gods had not also granted eternal youth. Tithonus never died, but he kept aging like any other mortal; eventually, he was so decrepit, disease-ridden, and demented that his life had become unbearable.
This type of concern is sometimes raised by those who don't have a clear picture of rejuvenation biotechnologies and fear that an extended period of frailty and decrepitude may be what scientists are after. Thankfully, quite the opposite is true, and, in fact, Tithonus' grim fate is physically impossible. In the fanciful realm of gods and myths, anything goes and the impossible becomes mundane, but in the real world, neither Zeus nor anyone else could make you live forever without eliminating or obviating the aging process. This is because death is nothing but the result of a critical failure of your inner workings - if you died, it means something crucial in your body stopped functioning properly and thus triggered a cascade of failure whose ultimate consequence was your death.
In particular, in the case of death by old age, the critical failure is caused by one or several pathologies resulting from a life-long process of damage accumulation. This process is slow but insidious, and it starts speeding up considerably after middle age. Frailty, weakness, and all the notorious diseases of old age are its primary consequences and are due to the fact that accumulated damage prevents your body from functioning at its best; when the damage is extensive enough, your body cannot function at all anymore. Living forever while aging forever would thus be equivalent to a human-made machine still functioning despite all of its mechanisms being eventually completely broken, which is a contradiction in terms.
A very small-scale version of Tithonus' myth does actually take place as a consequence of present-day geriatric medicine. Geriatric medicine focuses on treating the symptoms of age-related diseases rather than their causes, with the result of modestly improving patient health and lifespan - in other words, although with the best intentions, geriatrics does prolong the time patients spend in decrepitude. They live a little longer because mitigating the symptoms slightly postpones the inevitable, but as age-related damage keeps accumulating, eventually the point of no return is reached. It's a bit like trying to empty a river using a coffee mug.
Interventions for different types of age-related damage - such as senolytics for senescent cell clearance, enzyme replacement therapy to dispose of intracellular waste, and AGE-breaking molecules to eliminate extracellular cross-links - are currently being developed, and some are even undergoing human clinical trials. The aim of rejuvenation biotechnology is neither extending frailty nor achieving a modest amelioration of an elderly patient's health; rather, the goal is to comprehensively address age-related damage to allow people to maintain youthful levels of health for as long as they live, however long that may be.