A person's age estimated in terms of function.
The age of an individual expressed in terms of the chronological age of a normal individual showing the same degree of anatomical and physiological development.
Whitney E. Rolfes SR. Understanding Nutrition. 10th Edition. Belmont, CA: Thompson Wadsworth. 2005.
The American Heritage Stedman's Medical Dictionary, 2nd Edition. Boston, MA: Houghton Mifflin Company. 2004.
Dorland's Illustrated Medical Dictionary. Age. Philadelphia, PA: WB Saunders. 2004.