Left: results of the activity-rotation relation fitting for the three mass ranges considered in this work. Right: retrieved L_x-age relation from angular evolution models for the same mass bins together with M dwarfs with known ages from the literature by Wright et al. (2011) (blue points) and Veyette & Muirhead (2018) (squared cyan). The yellow region shows the vertical L_x-spread from the standard deviation of the observed L_x − P_rot relation. Three different initial rotation periods are shown: P_rot, 1 = 1.54 d (red line), P_rot, 2 = 5.51 d (blue line), and P_rot, 3 = 8.83 d (green line). In the predicted L_x-age relation we show the model for the central mass bin (solid line), together with the lower and upper mass boundaries (dashed and dotted line, respectively).