For most of medical history, age was a number you were handed at birth and could do nothing about. That era is ending. The clinics defining the frontier of longevity now measure a different figure entirely - your biological age, read from the epigenome, the cardiovascular system and the metabolism.
The distinction is not academic. Two individuals of the same chronological age can differ by two decades in biological terms, and it is the biological figure that predicts how the coming years will feel. The good news, and the reason this field has drawn such serious investment, is that biological age responds to intervention.
What separates a credible longevity programme from a fashionable one is rigour: a true baseline, precise intervention, and a protocol that continues after departure. The rest is theatre.
