  The Serpens Molecular Cloud is one of the most active star-forming regions
within 500 pc, with over one thousand of YSOs at different evolutionary stages.
The ages of the member stars inform us about the star formation history of the
cloud. In this paper, we develop a spectral energy distribution (SED) fitting
method for nearby evolved (diskless) young stars from members of the Pleiades
to estimate their ages, with a temperature scale adopted from APOGEE spectra.
When compared with literature temperatures of selected YSOs in Orion, the SED
fits to cool (<5000 K) stars have temperatures that differ by an average of <~
50 K and have a scatter of ~ 210 K for both disk-hosting and diskless stars. We
then apply this method to YSOs in the Serpens Molecular Cloud to estimate ages
of optical members previously identified from Gaia DR2 astrometry data. The
optical members in Serpens are concentrated in different subgroups with ages
from ~4 Myr to ~22 Myr; the youngest clusters, W40 and Serpens South, are dusty
regions that lack enough optical members to be included in this analysis. These
ages establish that the Serpens Molecular Cloud has been forming stars for much
longer than has been inferred from infrared surveys.
