Abstract: Chronological age (CA) is the actual age of an individual expressed in time during the period of experience since birth. However, CA may be inadequate in evaluating individual functional status. Therefore, more accurate measurement indicators are needed. Functional age reflects the actual age of individual organs or systems and can assess individuals' actual functional state and aging process more accurately than CA. However, due to the different starting points, concerns and disciplines of functional age researchers, the names of functional age are also different. This review mainly summarizes the functional age of different organ systems and the markers and methods used in the construction process. It divides the functional age into system/organ functional age and overall functional age. At the same time, it introduces the current clinical application status and guides the construction of a more accurate functional age.