Luminosity function of NGC 6231 (blue curve) based on the KDE. The kernel bandwidth is 0.30. The thin blue, orange, and green histograms represent the PARSEC LF models for 3.5, 4.5, and 5.5 Myr in M_G. The models are vertically re-scaled by a factor of 30 to compare with the luminosity function of NGC 6231. The dash-dotted blue vertical line indicates the position of the observed H-peak at M_G = 0.8 mag; the dashed red vertical line indicates the completeness limit at the bright end of Gaia DR2 at the distance of the cluster. The H-peak is within the completeness range of Gaia DR2. The position of the H-peak is consistent with the age determination of NGC 6231: 4.7 ± 0.4 Myr (van der Meij et al. 2021).