  Using the low limit of cosmic ages from globular cluster and the white
dwarfs: $t_0 > 12$Gyr, together with recent new high redshift supernova
observations from the HST/GOODS program and previous supernova data, we give a
considerable estimation of the equation of state for dark energy, with uniform
priors as weak as $0.2<\Omega_m<0.4$ or $0.1<\Omega_m h^2<0.16$. We find cosmic
age limit plays a significant role in lowering the upper bound on the variation
amplitude of dark energy equation of state. We propose in this paper a new
scenario of dark energy dubbed Quintom, which gives rise to the equation of
state larger than -1 in the past and less than -1 today, satisfying current
observations. In addition we've also considered the implications of recent
X-ray gas mass fraction data on dark energy, which favors a negative running of
the equation of state.
