The ionome is the elemental composition of a tissue, organ, or individual. This composition changes over the course of aging, and may do so in ways that allow the production of an aging clock, a measure of chronological or physiological age.
At the end of the day, all of these approaches need a great deal more validation if they are to be used as originally intended, as a way to rapidly assess potential rejuvenation therapies and thus speed up the field. Since it remains quite unclear as to what exactly these clocks measure, meaning which processes of aging cause the clock numbers to change, the results are not yet actionable.
Source: Fight Aging!