  Ages of the magnetar 1E 2259+586 and the associated supernova remnant CTB~109
were studied.
  Analyzing the Suzaku data of CTB~109, its age was estimated to be
$\sim$14~kyr, which is much shorter than the measured characteristic age of 1E
2259+586, 230 kyr. This reconfirms the previously reported age discrepancy of
this magnetar/remnant association, and suggests that the characteristic ages of
magnetars are generally over-estimated as compared to their true ages. This
discrepancy is thought to arise because the former are calculated without
considering decay of the magnetic fields. This novel view is supported
independently by much stronger Galactic-plane concentration of magnetars than
other pulsars. The process of magnetic field decay in magnetars is
mathematically modeled. It is implied that magnetars are much younger objects
than previously considered, and can dominate new-born neutron stars.
