  The existence of old high-redshift objects provides an important tool for
constraining the expanding age of the Universe and the formation epoch of the
first objects. In a recent paper, Hasinger {\it et al.} (2002) reported the
discovery of the quasar APM 08279+5255 at redshift $z=3.91$ with an extremely
high iron abundance, and estimated age of 2 - 3Gyr. By assuming the lower limit
for this age estimate and the latest measurements of the Hubble parameter as
given by the HST key project, we study some cosmological implications from the
existence of this object. In particular, we derive new limits on the dark
matter and vacuum energy contribution. Our analysis is also extended to
quintessence scenarios in which the dark energy is parameterized by a smooth
component with an equation of state $p_x = \omega_x \rho_x$ ($-1\leq \omega_x <
0$). For flat models with a relic cosmological constant we show that the vacuum
energy density parameter is constrained to be $\Omega_\Lambda \geq 0.78$, a
result that is marginally compatible with recent observations from type Ia
supernovae (SNe Ia) and cosmic microwave background (CMB). For quintessence
scenarios the same analysis restricts the cosmic parameter to $\omega_x \leq
-0.22$. Limits on a possible first epoch of quasar formation are also briefly
discussed. The existence of this object pushes the formation era back to
extremely high redshifts.
