Objectives The increasing problem of population aging requires appropriate economic and health‐related measures to mitigate its negative effects. The aim was to categorize the biological age of men between 20 and 70 years of age and assess its relationship to their physical activity and fitness. Methods Data included morphological variables, total body water, the results of five Eurofit motor tests and the percentage of maximum heart rate (HR%), during a cardiovascular test of more than 1,400 20–70 year‐old men living in Kraków. Biological age was estimated with regression equations. Results There were significant and consistent differences in physical fitness profiles between the three established groups of relations between biological and chronological age (biologically younger, equal, and older). These three categories of biological age were generally consistent with the regression analysis of physical fitness results, although declared physical activity seemed to be an independent factor. Conclusions The selected morphological variables represent a set of characteristics useful for the determination of the biological age. The existing relationship between physical activity and biological age indicates that physical activity may contribute to the inhibition of involutional changes, even if it had only been performed regularly in the past. Am. J. Hum. Biol. 28:503–509, 2016. © 2015 Wiley Periodicals, Inc.