  We present estimates of stellar age and mass for 0.93 million Galactic disk
main sequence turn-off and sub-giant stars from the LAMOST Galactic
Spectroscopic Surveys. The ages and masses are determined by matching with
stellar isochrones using Bayesian algorithm, utilizing effective temperature
$T_{\rm eff}$, absolute magnitude ${\rm M}_V$, metallicity [Fe/H] and
$\alpha$-element to iron abundance ratio [$\alpha$/Fe] deduced from the LAMOST
spectra. Extensive examinations suggest the age and mass estimates are robust.
The overall sample stars have a median error of 34 per cent for the age
estimates, and half of the stars older than 2\,Gyr have age uncertainties of
only 20--30 per cent. Median error for the mass estimates of the whole sample
stars is $\sim8$ per cent. The huge dataset demonstrates good correlations
among stellar age, [Fe/H] ([$\alpha$/H]) and [$\alpha$/Fe]. Particularly,
double sequence features are revealed in the both the age--[$\alpha$/Fe] and
age--[Fe/H]([$\alpha$/H]) spaces. In the [Fe/H]--[$\alpha$/Fe] space, stars of
8--10\,Gyr exhibit both the thin and thick disk sequences, while younger
(older) stars show only the thin (thick) disk sequence, indicating that the
thin disk became prominent 8--10\,Gyr ago, while the thick disk formed earlier
and almost quenched 8\,Gyr ago. Stellar ages exhibit positive vertical and
negative radial gradients across the disk, and the outer disk of
$R\gtrsim$\,9\,kpc exhibits a strong flare in stellar age distribution.
