People have looked for such things. https://en.wikipedia.org/wiki/Epigenetic_clock https://en.wikipedia.org/wiki/Epigenetic_clock describes the best one found.

People have looked for such things. https://en.wikipedia.org/wiki/Epigenetic_clock https://en.wikipedia.org/wiki/Epigenetic_clock describes the best one found. But, unfortunately, all the ones we know of can be skewed by environmental factors. And it is likely that the exact same environmental factors which make someone live longer will also make them appear younger than they are. Which makes them particularly unreliable exactly for the oldest people on record.