Backward evolution of the mass-weighted age vs. stellar mass relation (computed at z = 2.2, z = 0.8, and z = 0.4) for the galaxies which lie on the MZR of Kewley & Ellison (2008) and on the MSR as derived by Peng et al. (2010). The color-coding indicates the loading factor parameter λ. The white-grey contour lines indicate isodensity contours. The shaded pink area indicates the observational data by Trussler et al. (2020) for local star-forming galaxies (0.02 <  z <  0.085), whereas the shaded blue area stands for the relation obtained using the SDSS-DR7 catalog of mass-weighted ages estimated as in Gallazzi et al. (2008) using the same selection of star-forming galaxies as Trussler et al. (2020). In the upper panel, the black points are the mean age values of the simulated galaxies at redshift z ∼ 0.1 inside bins of size 0.5 log(M_⋆/M_⊙) and the error bars are the standard deviations.