Smoothed stellar population properties of quiescent galaxies for EMILES SSP models and Padova00 isochrones at 0.3 ≤ z <  0.5 as a function of their positions in the stellar mass–size plane (coloured dots, see colour bar in each panel). Top panels, from left to right: mass-weighted formation epoch, age, and metallicity, and bottom panels: extinction, luminosity surface brightness in the I band, and Sérsic index, respectively. To guide the eye, we illustrate the curve of constant formation epoch (black solid line) and its uncertainty (shaded area), as well as the stellar mass–size relation at this redshift bin (dotted black line).