  Age is the most difficult fundamental stellar parameter to infer for isolated
stars. While isochrone-based ages are in general imprecise for both main
sequence dwarfs and red giants, precise isochrone-based ages can be obtained
for stars on the subgiant branch transitioning from core to shell hydrogen
burning. We synthesize Gaia DR3-based distance inferences, multiwavelength
photometry from the ultraviolet to the mid infrared, and three-dimensional
extinction maps to construct a sample of 289,759 solar-metallicity stars
amenable to accurate, precise, and physically self-consistent age inferences.
Using subgiants in the solar-metallicity open clusters NGC 2682 (i.e., M 67)
and NGC 188, we show that our approach yields accurate and physically
self-consistent ages and metallicities with median statistical precisions of
8\% and 0.06 dex. The inclusion of systematic uncertainties resulting from
non-single or variable stars results in age and metallicity precisions of 9\%
and 0.12 dex. We supplement this solar-metallicity sample with an additional
112,062 metal-poor subgiants, including over 3,000 stars with
$[\text{Fe/H}]\lesssim-1.50$, 7\% age precisions, and apparent Gaia $G$-band
magnitudes $G<14$. We further demonstrate that our inferred metallicities agree
with those produced by multiplexed spectroscopic surveys. As an example of the
scientific potential of this catalog, we show that the solar neighborhood
star-formation history has three components at $([\text{Fe/H}],\tau/\text{Gyr})
\approx (+0.0,4)$, $(+0.2,7)$, and a roughly linear sequence in
age--metallicity space beginning at
$([\text{Fe/H}],\tau/\text{Gyr})\approx(+0.2,7)$ and extending to $(-0.5,13)$.
Our analyses indicate that the solar neighborhood includes stars on disk-like
orbits even at the oldest ages and lowest metallicities accessible by our
samples.
