Relation between the SN Ia rate model and the average age of the stars in the parent galaxy, for exponentially declining SFHs and a DDC model description of the DTD. The different solid lines are obtained for different values of the e-folding SF timescale, ranging from 0.1 Gyr (lowermost curve) to 8 Gyr (uppermost curve). Along each line the parameter AGE increases from 0.05 to 12.5 Gyr. The dashed and dotted lines are drawn at the median average ages, respectively, of the least and the most massive bin in Fig. 14.