Transhumanists and their fellow travelers urge humanity to prioritize the development of biotechnologies that would eliminate aging, delivering ‘an endless summer of literally perpetual youth.’ Aspiring not to age instantiates what philosopher Martha Nussbaum calls the yearning for ‘external transcendence,’ or the fundamental surpassing of human bounds due to confidence that life without them would be better. Based on Immanuel Kant’s account of the parameters of human understanding, I argue that engineering agelessness could not be a rational priority for humanity (...) on the level of public policy. This stance is complemented by an argument focused on individual decision-making in liberal-democratic milieus, where no governing conception of the good is presumed and the first-personal level matters greatly. Here, drawing on philosopher and cognitive scientist Laurie Ann Paul’s concept of ‘transformative experience,’ I maintain that individuals could not ‘rationally,’ meaning, here, ‘prudentially,’ say ‘yes’ to agelessness. Absorbing the irrationality of human zeal to eliminate aging, based on assurance that an ageless existence would be better, should spur a redoubled dedication to human flourishing. (shrink)