  Detailed modelling of stellar oscillations is able to give precise estimates
for stellar ages, but the inferred results typically depend on the adopted
model parameters used for the age inference. High-quality asteroseismic data
with precise measurements of mixed modes are available for 36 Kepler subgiants.
To obtain a handle on the robustness of the ages for these stars, we first
study the dependencies of seismic ages on three model input parameters. We find
that inferred ages do not change systematically with the helium fraction (Y) or
the mixing-length parameter but depend strongly on the metallicity ([M/H]) of
the model. The results indicate that age estimates of subgiants have less model
dependence and hence are more reliable than those of main-sequence stars or red
giants. We then model individual oscillation frequencies of the same 36 Kepler
subgiants, using observed metallicities, and obtain their ages with an average
precision of ~15%. The comparison with previous age estimates with different
stellar codes or input physics shows good agreement (mostly within 2#). We
hence suggest that seismology-determined ages of subgiants are not greatly
model-dependent.
