impose on $w(z)$. As a consistency check we note that the age at $z=0$ obtained here is in good agreement with GC ages (see §2) and that the Treu et al.galaxy ages agree with those from of SDSS LRG sample where they overlap. The solid line in Figure 4 corresponds to the age–redshift relation for our flat, reference $\Lambda$CDM model: $\Omega_m=0.27$, $h=71$, and $w=-1$. This is consistent with the observed age–redshift envelope, and it seems to indicate that we live in a universe with a classical vacuum energy density and that, on average, stars in the oldest galaxies formed about 0.7 Gyr after the Big Bang (e.g., at redshifts $z \sim 7-10$). To make the observed age–redshift relation consistent with a model with widely different $w(z)$ behavior, we would have to infer that early-type galaxies at different redshifts have very different formation epochs for their stellar populations. For example, the dotted line in Figure 4 indicates the age-redshift relation for an evolving population in a universe where $w(z)=-2$ for $z > 1$ and grows linearly from $w=-2$ at $z=1$ to $w=0$ at $z=0$. For this model to work, we would have to conclude that the oldest galaxies at $z\sim 1.5$ 