Four representative examples of mass-weighted stellar age maps. For display purposes, we show for all galaxies a central area of the same 50 kpc  ×  20 kpc size. Horizontal dashed black lines indicate the regions where the thin disk (within the two lines) and the thick disk dominate (above and below the region between the two lines). Vertical dashed black lines enclose the central region dominated by a bar or a classical bulge. Names of the AURIGA halos are indicated on top of each panel. Ages were integrated and projected into pixels of 0.5 kpc  ×  0.5 kpc size and Voronoi binned to obtain at least 900 star particles per bin. Maps of the full sample are shown in Appendix B.2.