CMD showing the separation of the massive stars into two age groups. The complete sample of stars is indicated in grey, the younger massive stars are indicated in blue, and the older massive stars are indicated in red. Isochrones from the Padova group (see, e.g., Marigo et al. 2017, and references therein) for ages of 10, 20, 30, 60, and 80 Myr are indicated in solid lines in shades of grey, with corresponding numbers in the image. Additionally, an isochrone for an age of 4 Gyr is indicated by a dashed black line.