For the first time, six proteomic aging clocks have been deployed as readouts in a clinical trial, enabling real-world testing of biomarker behavior and performance. The study aims to clarify strengths and weaknesses of the clocks themselves, independent of the therapeutic effect under evaluation. This is a significant step for the “aging biomarkers” field because proteomic clocks can be sensitive to confounding factors like treatment effects, inflammation, and sample handling variability. A clinical trial context provides the needed stress test to assess repeatability, interpretability, and practical utility. If the clocks demonstrate robustness and meaningful signal, they could become more routine tools for monitoring biological age modulation in future development programs.