Physical aging commonly refers to slow, irreversible relaxation observed in materials far from equilibrium. Here, I will outline a unified framework based on our experiments with diverse mechanical systems, including frictional interfaces, crumpled sheets, elastic foams, and silica aerogels. Multi-step loading protocols lead to nonmonotonic responses and memory effects that reveal hidden internal state parameters. These phenomena are captured well by the Amir–Oreg–Imry (AOI) model of broadly distributed modes, establishing a new universality class for aging systems.  For systems in this universality class, aging does not necessarily suggest irreversibility; instead, it can arise from the constrained redistribution of stored energy across a large hierarchy of scales. AOI has an intrinsic symmetry between conjugate variables, however, if the elasticity is nonlinear, force and displacement become non-interchangeable, and in systems like crumpled sheets, relaxation occurs exclusively through force modes. Speckle holography in aerogels resolves the microstructural dynamics and shows that over many decades in time they are largely reversible, a mechanism that is likely relevant from complex fluids to architected solids. This suggests that for many systems, aging should be viewed less as irreversible creep and more as a reversible reconfiguration of the system’s internal state.