[C/N] versus age for the RC stars. The dots represent the averaged [C/N] values and the scatter per cluster of this work and the obtained relation with the age (black continuous line). The clusters shown without scatter bars contain only a single investigated star. For a comparison, the corresponding data and relation obtained in the Gaia-ESO survey, determined using the same method of analysis, are shown by the triangles and dashed black line (Tautvaišienė et al. 2025). The dashed green line represents the theoretical relation by Lagarde et al. (2017).