19. Are epigenetic changes causes of aging or readouts?

Both, depending on context. Many epigenetic changes are readouts of upstream damage burden and adaptation, while some can become causal by locking in altered gene regulation and cell identity. In a systems view, epigenetic state is a major layer through which deleteriome components are integrated and propagated; causality is distributed and may be amplified (damage → epigenetic drift → dysfunction → more damage). A practical question is which epigenetic changes are reversible, and which ones reflect irreversible constraints.