Flaring activity measure β_100s for the FFDs in Fig. 4 as a function of age. The values are grouped by T_eff (different colors and symbols in the legend), and presented on a log-log scale. β_100s indicates the occurrence rate of flares with ED >  100 s (see Eq. (3)). It is controlled for stellar luminosity, so that we can compare flaring activity across both age, and T_eff, at the same time. The age labels correspond to the open cluster ages in Table 1.