Median maximum Galactic height, 〈Z_max〉, versus the median stellar age, t_★, for all disc stars in the six groups, ordered by decreasing metallicity from top left to bottom right. This image is similar to Fig. 14, with adjacent 1D-Gaussian kernel distributions helping the visualisation of the distribution of both parameters and horizontal lines indicating the scale heights for the thin and thick discs (dashed and dot-dashed lines respectively). A vertical line is added at t = 6 Gyr to flag the time of the first pericentric passage of Sagittarius. Age uncertainties are not displayed to improve visualisation, but typical errors are of 2 Gyr (Mints & Hekker 2018). It is noticeable the increase in the proportion of stars with larger 〈Z_max〉 with decreasing metallicities (i.e. groups 5, 4, and 3), and thus we have included the standard deviation of both parameters (${\overline{t}}_{\star }$ and σ_Zmax) for each group in the top left corner. Both standard deviations tend to increase as 〈[Fe/H]〉 decreases.