  We present a study of 33 {\it Kepler} planet-candidate host stars for which
asteroseismic observations have sufficiently high signal-to-noise ratio to
allow extraction of individual pulsation frequencies. We implement a new
Bayesian scheme that is flexible in its input to process individual oscillation
frequencies, combinations of them, and average asteroseismic parameters, and
derive robust fundamental properties for these targets. Applying this scheme to
grids of evolutionary models yields stellar properties with median statistical
uncertainties of 1.2\% (radius), 1.7\% (density), 3.3\% (mass), 4.4\%
(distance), and 14\% (age), making this the exoplanet host-star sample with the
most precise and uniformly determined fundamental parameters to date. We assess
the systematics from changes in the solar abundances and mixing-length
parameter, showing that they are smaller than the statistical errors. We also
determine the stellar properties with three other fitting algorithms and
explore the systematics arising from using different evolution and pulsation
codes, resulting in 1\% in density and radius, and 2\% and 7\% in mass and age,
respectively. We confirm previous findings of the initial helium abundance
being a source of systematics comparable to our statistical uncertainties, and
discuss future prospects for constraining this parameter by combining
asteroseismology and data from space missions. Finally we compare our derived
properties with those obtained using the global average asteroseismic
observables along with effective temperature and metallicity, finding an
excellent level of agreement. Owing to selection effects, our results show that
the majority of the high signal-to-noise ratio asteroseismic {\it Kepler} host
stars are older than the Sun.
