Predicted age versus input age in different magnitude bins. The median μ and σ_NMAD of the residuals (Δ= output – input) are reported for the full sample and for the three age ranges delimited by the dashed vertical lines. Red points indicate the median values in age bins, with red error bars showing the interquartile range (25th to 75th percentiles) of the distribution. Symbols are colour-coded by number density (more populated regions are plotted in yellow). The upper-left panel shows the results for all the test sample, while the other three panels are limited to a given i magnitude bin, stated in the legend. The typical S/N in the narrow-band filters is also reported.