Chronological Age

Definition

Chronological age is the elapsed time since birth, typically measured in years, and serves as the standard temporal reference in demographic, clinical, and epidemiologic studies. It is a calendar-based index rather than a direct measure of physiological state or functional capacity.[1][2]

Why It Is Limited

Chronological age does not capture heterogeneity in health status, functional capacity, or biological ageing rates. Individuals of the same chronological age can follow divergent trajectories due to genetic, environmental, and lifestyle factors, which limits its precision for individual-level risk assessment.[1][2]

Use in Ageing Studies

Chronological age remains a useful covariate and baseline for population-level risk estimates, but it is increasingly paired with biological age indicators to better explain inter-individual variability in disease risk and functional outcomes.[1][3]

References

1. Salih, A., et al. (2023). Conceptual overview of biological age estimation. https://pmc.ncbi.nlm.nih.gov/articles/PMC10187689/
2. Baars, J. (2013). Aging and Time. http://www.janbaars.nl/wp-content/uploads/Aging-and-Time-Chapter-01-Jan-Baars.pdf
3. Witzel, D. D., et al. (2025). Age and inflammation: Insights on "age three ways" from population cohorts. https://www.sciencedirect.com/science/article/abs/pii/S0889159125001035