6. Why does aging impose an arrow of time inside organisms?

Aging gives time a direction because it leaves an accumulating record: the deleteriome is a distributed memory of irreversible processes, e.g. chemical modifications, structural drift, epigenetic and proteostatic remodeling, clonal expansions, ecological shifts, and lost options; that cannot be perfectly unwound by finite control systems in a finite time. Even when damage is repaired or overwritten, an organism is not returned to a previous microstate; it becomes a new state with a different history, and some changes are not simply erasable without replacement (e.g., accumulated somatic mosaicism, scar-like remodeling, extinct cell states, altered niches). This is why age reversal is best framed as lowering biological age. The arrow persists because the underlying process is a sequence of irreversible transformations that cannot be shortcut without cost; what we can do, in practice, is reduce the rate of recording, repair or replace parts of the record, and rebuild buffering capacity.