Upper envelope of the age–metallicity relation traced for the stars with asteroseismic ages from Miglio et al. (2021) and [Fe/H] from the APOGEE DR17 catalogue (Abdurro’uf et al. 2022). The triangles represent the median [Fe/H] of five (red) and ten (black) most metal-rich stars in each age bin, and the error bars show the scatter in [Fe/H]. A smaller number of stars per bin, for median and scatter, are used due to the smaller number of stars in the Miglio et al. (2021) catalogue.