T_eff-log g (left) and T_eff-M_Ks (right) diagrams for a few cherry-picked open clusters. The isochrones of the adopted mean age (in red) and the reference age from Cantat-Gaudin et al. (2020) are plotted in red and black, respectively, for the mean metallicity of the cluster derived from the calibrated GSP-Spec values. The first two rows show examples for which our ages and the literature values are in good agreement. The bottom two rows show the opposite: for NGC2112 our solution fits the data better than the younger isochrone, pointing towards offsets in the input T_eff, [M/H], or distance modulus. For NGC7789, our solution is not reliable, since main-sequence stars do not constrain the ages well enough.