What Would Count as Proof of Rejuvenation?

A yardstick for epigenetic reprogramming claims: four outcome levels, five evidence tiers, and why a younger clock is where the question starts

Abstract

Claims that aging can be reversed have moved from speculation into laboratories, company pipelines and, in 2026, a first-in-human trial. The most discussed approach is partial epigenetic reprogramming: briefly switching on a few of the genes that can return adult cells to an embryonic-like state, in the hope of restoring youthful function withou…