Top left: simulated cumulative distribution of two planetary samples at 5 Gyr (dashed line) and 100 Myr (solid line). The two dotted lines are the computed cumulative radius distribution at 100 Myr, assuming volatile-poor (upper curve) and volatile-rich (lower curve) planets. Top right: radius of a 12 M_⊕ planet as a function of the gas fraction. The upper curve is computed assuming a volatile fraction f_vol = 70%, while the lower curve shows dry planets (f_vol = 0). Bottom left: cumulative distribution of the gas fraction for volatile-rich planets (hypothesis 1) and volatile-poor planets (hypothesis 2). Bottom right: observed cumulative distributions of radius at 100 Myr (thick cyan line), at 5 Gyr (thick green line). The two sets of red and blue lines are the computed cumulative radius distribution at 100 Myr assuming volatile-rich planets (hypothesis 1, blue dotted curve) or volatile-poor planets (hypothesis 2, red dotted curve).