Age dependence of R_g and [Fe/H] for the metal-rich stars. Left panel: stellar ages as a function of guiding radii for stars with [Fe/H] > 0.1 dex. The colours represent the number of stars per bin. A kernel density estimate (KDE) is overplotted. A dashed black line at 2.7 Gyr is also shown. Right panel: Upper envelope of the age–metallicity relation traced by our full sample. The triangles represent the median [Fe/H] of the 20 most metal-rich stars in each age bin and the error bars show the scatter in [Fe/H].