Chronological age refers to the period that has elapsed beginning with an individual's birth and extending to any given point in time. Chronological age is used in research and in test norm development as a measure to group individuals. Developmental research looks for age-related differences or behavior changes as a function of age.
Using chronological age provides a means to roughly assure the equivalence of such factors as physical experience, social interaction, learning, and acculturation among others. Chronological age is not necessarily a predictor of an individual's stages of development, as the rate at which individual's progress through stages may not be identical. Problems in using chronological age include such issues as school readiness and the evaluation of premature infants. As medical technology has advanced in the treatment of premature infants, chronological age has been challenged as an appropriate measure for this group with gestational age or durational pregnancy being proposed as a means of adjusting chronological age.
du Toit, M. K. "A Life-Span Developmental Orientation: The Relevance of Chronological Age in Life-Span Developmental Psychology: A Theoretical Observation." South African Journal of Psychology 22 (1992):21-26
Kraemer, Helena, Anneliese Korner, and Shelley Horwitz. "AModel for Assessing the Development of Preterm Infants as a Function of Gestational, Conceptual, or Chronological Age." Developmental Psychology 21 (1985):806-812.