Beyond lifespan and healthspan: a biological framework for experienced longevity

Aging research has traditionally focused on lifespan and healthspan as primary outcome domains, implicitly treating chronological time as a uniform container of value. The memory-structured reconstruction of extended chronological intervals has not been systematically examined as an aging-related variable. I introduce experienced longevity, defined as the amount of lived time subjectively contained within a fixed chronological interval. Drawing on established distinctions between retrospective and prospective duration judgments, I argue that long-interval temporal compression reflects memory-structured reconstruction rather than altered internal timekeeping. Building on event segmentation theory, I propose that experiential density - the number and distinctiveness of retrievable experience units per unit time - determines whether extended intervals are remembered as compressed or expanded. I present the Neuroenergetic Constraint Model, which posits that aging-related reductions in mitochondrial efficiency, increased vascular stiffness, and diminished nitric oxide-mediated neurovascular coupling constrain neuroenergetic flexibility. Reduced energetic reserve may limit high-fidelity updating during ongoing experience, weaken event segmentation, decrease experiential density, and increase the probability of retrospective temporal compression. The model generates falsifiable predictions linking biological markers of neuroenergetic reserve (e.g., metabolic efficiency, arterial stiffness, endothelial function) to segmentation performance and retrospective duration judgments, particularly under high-demand conditions. If supported, this framework expands aging science beyond survival and function to include the biological structuring of lived time.