Column-normalised 2D histograms of the stellar age distribution, τ_⋆(R), for the LAMOST-DR3 (left) and APOGEE-DR17 (right) samples. The red and green markers show the mean and median profiles, respectively. The solid curves show the age profile resulting from the maximum-likelihood fitting (this fits to all individual sources without binning – see text for details). In each panel, we also cross-plot the ML fit of the dataset in the opposite panel for comparison. The black marker reflects the location of the maximum-likelihood age minimum and associated uncertainty.