  We present abundances of 21 elements in a sample of 13 bright FG dwarfs drawn
from the Kepler LEGACY sample to examine the applicability of the abundance-age
relations to stars with properties strongly departing from solar. These stars
have precise asteroseismic ages that can be compared to the abundance-based
estimates. We analyse the well-known binary 16 Cyg AB for validation purposes
and confirm the existence of a slight metal enhancement (~0.02 dex) in the
primary, which might arise from planetary formation/ingestion. We draw
attention to systematic errors in some widely-used catalogues of non-seismic
parameters that may significantly bias asteroseismic inferences. In particular,
we find evidence that the ASPCAP Teff scale used for the APOKASC catalogue is
too cool for dwarfs and that the [Fe/H] values are underestimated by ~0.1 dex.
We compare seismic ages to those inferred from empirical abundance-age
relations based on ages from PARSEC isochrones and abundances obtained in the
framework of the HARPS-GTO program. These calibrations take into account a
dependency with the stellar effective temperature, metallicity, and/or mass. We
find that the seismic and abundance-based ages differ on average by 1.5-2 Gyrs,
while taking into account a dependency with one or two stellar parameters in
the calibrations leads to a global improvement of up to ~0.5 Gyr. However, even
in that case we find that seismic ages are systematically larger by ~0.7 Gyr.
We argue that it may be ascribed to a variety of causes including the presence
of small zero-point offsets between our abundances and those used to construct
the calibrations or to the choice of the set of theoretical isochrones. The
conclusions above are supported by the analysis of literature data for a larger
number of Kepler targets. [Abridged]
