  We investigate the precision of the ages and metallicities of 21,000 mock
simple stellar populations (SSPs) determined through full-spectrum fitting. The
mock SSPs cover an age range of 6.8 $<$ log (age/yr) $<$ 10.2, for three
wavelength ranges in the optical regime, using both Padova and MIST isochrone
models. Random noise is added to the model spectra to achieve S/N ratios
between 10 to 100 per wavelength pixel. We find that for S/N $\geq$ 50, this
technique can yield ages of SSPs to an overall precision of
$\Delta\,\mbox{log(age/yr)} \sim 0.1$ for ages in the ranges 7.0 $\leq$ log
(age/yr) $\leq$ 8.3 and 8.9 $\leq$ log (age/yr) $\leq$ 9.4. For the age ranges
of 8.3 $\leq$ log (age/yr) $\leq$ 8.9 and log (age/yr) $\geq$ 9.5, which have
significant flux contributions from asymptotic giant branch (AGB) and red giant
branch (RGB) stars, respectively, the age uncertainty rises to about $\pm 0.3$
dex. The precision of age and metallicity estimation using this method depends
significantly on the S/N and the wavelength range used in the fitting. We
quantify the systematic differences in age predicted by the MIST and Padova
isochrone models, due to their different assumptions about stellar physics in
various important (i.e., luminous) phases of stellar evolution, which needs to
be taken in consideration when comparing ages of star clusters obtained using
these popular models. Knowing the strengths and limitations of this technique
is crucial in interpreting the results obtained for real star clusters and for
deciding the optimal instrument setup before performing the observations.
