Yang et al. unveiled a transcriptomic atlas delineating young and aged livers from healthy cynomolgus monkeys at a single-cell resolution. Their study delved into the specific gene expression alterations within distinct cell types and the microenvironmental circuitry influencing hepatic aging phenotypes. The liver, akin to a mosaic of puzzle pieces, embodies various cell types. With certain puzzle pieces absent, the underlying clock is exposed, illustrating age-related changes within the liver.