Science at the state level consists of two distinct and heterogeneous systems: the global science system and national science systems. National science systems are deeply embedded in global science, and states seek to use global knowledge for domestic economic needs. However, harnessing the wealth of global knowledge can only be done through scientists. Consequently, the scientific strength of states in practice depends on the scientific strength of individual scientists. Their ability to collaborate internationally and to tap into the global scientific network is crucial. By remaining outside it and working within local research programs, the academic community risks being marginalized, losing the interest of national research funding patrons, and losing the ability to influence the development of science.

In this text, we analyze the limitations of using academic age as a proxy for biological age in the whole national science system, for which we consider both biological age and academic age of all researchers from all Polish universities, holding at least a PhD degree and participating in global academic science through international publications (N = 20 569). An approximation of a researcher's functioning in global science is having at least one publication indexed in the Scopus database in the analyzed decade 2009–2018. Thus, using the example of comprehensive data from the entire national system of science, we estimate the extent of limitations of using academic age as a proxy for biological age depending on selected independent variables and analyze both the practical and methodological implications of using academic age in academic career research, which is one of the most important components of quantitative studies of science.