A review by Cheema et al. published in The Journal of Clinical Investigation (JCI) maps the landscape of **biological age** (BA) measurement, tracing methods from functional tests and blood biomarkers to **epigenetic**, **proteomic**, **imaging**, **wearable**, and **AI-based** clocks, including first- through third-generation epigenetic clocks (examples: Horvath, Hannum, PhenoAge, GrimAge, DunedinPACE), per the review (JCI 2026;136(12):e205777, doi:10.1172/JCI205777). The authors report that ne