  We have measured Lick index equivalent widths to derive luminosity weighted
stellar ages and metallicities for thin and thick disk dominated regions of 9
edge-on disk galaxies with the ARC 3.5 meter telescope at Apache Point
Observatory. In all cases, the thick disks are confirmed to be old stellar
populations, with typical ages between 4 and 10 Gyr. The thin disks are
uniformly younger than the thick disks, and show strong radial age gradients,
with the outer regions of the disks being younger than 1 Gyr. We do not detect
any significant metallicity differences or alpha-element enhancement in the
thick disk stars compared to the thin disk, due to the insensitivity of the
Lick indices to these differences at low metallicity. We compare these results
to thick disks measured in other systems and to predictions from thick disk
formation models.
