Put it simply, there is reversible damage and irreversible damage. Oxidized protein aggregates that the cell can’t degrade are an example of irreversible aggregates. Amyloid protein fibrils, although no longer implicated in disease, are another example of a stable, irreversible state. The process of repair slows down not due to programming but because the cells of the body get progressively worse at identifying and repairing damage, because the very machinery that carries out these processes, proteins, get damaged.