  Dark energy is the invisible fuel that seems to drive the current
acceleration of the Universe. Its presence, which is inferred from an
impressive convergence of high-quality observational results along with some
sucessful theoretical predictions, is also supported by the current estimates
of the age of the Universe from dating of local and high-$z$ objects. In this
work we study observational constraints on the dark energy equation of state
($w$) from lookback time measurements of high-$z$ galaxies, as recently
published by the Gemini Deep Deep Survey (GDDS). In order to build up our
lookback time sample from these observations we use 8 high-$z$ galaxies in the
redshift interval $1.3 \leq z \leq 2.2$ and assume the total expanding age of
the Universe to be $t_{0}^{obs} = 13.6^{+0.4}_{-0.3}$ Gyr, as obtained from
current cosmic microwave background data. We show that these age measurements
are compatible with values of $w$ close to -1, although there is still space
for quintessence ($w > -1$) and phantom ($w < -1$) behaviors. In order to break
possible degeneracies in the $\Omega_{\rm{m}} - w$ plane, we also discuss the
bounds on this parametric space when GDDS lookback time measurements are
combined with the most recent SNe Ia, CMB and LSS data.
