  Fast radio bursts (FRBs) are mysterious radio transients with millisecond
durations. Recently, a periodic activity of $\sim$16 day and a possible
periodicity of $\sim$159 day were detected to arise from FRB 180916.J0158+65
and FRB 121102, respectively, and the spin period of a slow-rotation magnetar
was further considered to be one of possibilities to explain the periodic
activities of repeating FRBs. For isolated neutron stars, the spin evolution
suggests that it's difficult to reach several hours. In this work, we mainly
focus on the possible maximum spin period of isolated NSs / magnetars dominated
by an interaction between star's magnetic field and the disk. We find that the
disk wind plays an important role in spin evolution, whose influence varies the
power law index in the evolution equation of mass flow rate. For a magnetar
without disk wind, the longest spin period is tens of hours. When the disk wind
with a classical parameter is involved, the maximum spin period can reach
hundreds of hours. But for a much extremely large index of mass flow rate due
to disk wind or other angular momentum extraction processes, a spin period of
$\sim$(16-160) days is still possible.
