Age dependent activity indicators. Colour and line shapes distinguish different T_eff bins. Detection thresholds are derived from synthetic flare injections and averaged in each bin. For M 67, available upper limits are given with arrows. The highest energy we detect is ∼6 × 10³⁴ erg. Top panel: flare rate FR; centre: absolute flare luminosity in the Kepler band L_Kp, flare. Bottom panel: flaring activity FA (see definitions in Sect. 4.2). Grey dotted lines indicate the Skumanich age^−1/2 law for comparison.