Photometric magnetic activity level, ⟨ S_{ph,k = 5} ⟩, as a function of grid-modelling asteroseismic ages (in grey) taken from Chaplin et al. (2014). Stars have been divided into hot (red), dwarf (blue), and subgiants (green) as defined in Fig. 3. Only stars with P_rot ≥ 5 days are shown. Because of the size of the error bars, they are only plotted for each category of stars. The solar value of ⟨ S_{ph,k = 5} ⟩ = 166.1 ± 2.6 ppm for an age of 4.57 Gyr is represented with the solar symbol and the same colour code as in Fig. 4. The left and right dashed vertical lines correspond to the solar magnetic activity level at minimum and maximum of the 11 year solar cycle. The horizontal dotted lines mark the 2 Gyr limit.