  Glitches are common phenomena in pulsars. After each glitch, there is usually
a permanent increase in the pulsar's spin-down rate. Therefore a pulsar's
present spin-down rate may be much higher than its initial value. Thus the
characteristic age of a pulsar based on its present spin-down rate and period
may be shorter than a pulsar's age. At the same time, the permanent increase of
its spin-down rate implies that the pulsar's surface magnetic field is
increased after each glitch. Consequently after many glitches some radio
pulsars may evolve into AXPs and SGRs, i.e., strongly magnetized and slowly
rotating neutron stars.
