Age–velocity dispersion relation for PNe in the M 31 disc at R_GC = 14–17 and 17–20 kpc is shown in magenta and cyan, respectively. The assigned age is shown in log scale with the MS (∼30 Myr age; D15) in the R_GC = 14–17 kpc bin shown at 0.8 Gyr for visual clarity. The AVR obtained in the solar neighbourhood in the MW (Nordström et al. 2004) is shown in grey for comparison. Their total velocity dispersion is shown with squares while the velocity dispersion in the space velocity components (U, V, W) is shown with filled circles, open circles, and filled triangles, respectively. We also present, with open triangles, the velocity dispersion in the W component from Aniyan et al. (2018) for only those MW stars with [Fe/H] <  −0.3, showing a flattening in the MW AVR at older ages.