Your remark about the narrow age ranges as being too monolithic highlights an issue that plagues the omics-based biological clocks: while there are measurable omics changes that can align so closely with calendar age, that it is tempting to use those molecular markers to measure biological age, we still have no idea what many of those changes mean in terms of physiology and function. It is also less than clear whether modifying the underlying molecular pathways has any appreciable effect on function.