Host star’s evolutionary tracks in the SwoP scenario. Top panel: Surface-rotation-rate evolution versus age for our optimal stellar model, with Ω_in = 1, 2, 3.2, 4, 5, 6, 7, 8, 9, 10, 18 Ω_⊙. The dashed red line shows the evolution of the critical rotation velocity (Ω_crit), defined as the velocity at which the centrifugal acceleration at the equator equals the gravity. The magenta and black markers show GJ 504’s surface rotation rate, with age uncertainties derived from the global and local minimisation modelling, respectively. Middle panel: Evolution of stellar Rossby number (R_O). R_O for GJ 504 is indicated by the red, black, and blue circles corresponding to the lower, mean, and upper values of the largest age uncertainty, respectively. The grey and black stars represent the values obtained from τ_conv as in Wright et al. (2011) and Wright et al. (2018). Analogously, the magenta markers represent the same quantities for the smallest age uncertainty. Bottom panel: Evolution of X-ray luminosity for each of the considered rotators. The black and blue markers show the X-ray luminosities from Voges et al. (1999), Wright et al. (2011) (ROSAT) and in this work (eROSITA), respectively. Analogously, the magenta markers represent the same quantities for the smallest age uncertainty. In all panels, the starting point of the tracks corresponds to the dissipation of the protoplanetary disc (2 Myr for Ω_in = 18 Ω_⊙; 6 Myr for the other ones).