Is age really just a number? Hundreds of “aging clocks” developed over the last 10–15 years suggest that it is. These clocks aim to measure biological age rather than chronological age—initially using DNA methylation, more recent examples use, e.g., blood proteins. A recent preprint goes a step further by developing “tissue clocks” that predict the biological age of different human tissues from images or even blood samples. The authors reason that tissue structure, with its direct links to physiological fitness,…
