Distribution of star ages for increasing mass intervals. Each row corresponds to a decreasing mass interval (from 1 to 1.2 M_⊙ for the first row, 0.9 to 1.0 M_⊙ for the second row, 0.8 to 0.9 M_⊙ for the third row and 0.6 to 0.8 M_⊙ for the last row). The colours of the histograms correspond to the different regions of Figure 6. For each of these histograms, a line of the same colour is drawn to represent the median of the histogram.