Calculated age distribution of GCR protons with some fixed energies in the solar system for the case of . The thick line, the long-dashed line, and the thin line indicate the age distribution of protons which arrive at the solar system with a fixed energy of 100 MeV, 10 GeV, and 1 TeV, respectively. The dotted line indicates the age distribution expected by the leaky box model with the escape lifetime of 20 Myr.