  We examine the relation between stellar mass, velocity dispersion, size,
S\'ersic index and $D_n4000$ for ~40,000 quiescent galaxies in the SDSS. At a
fixed stellar mass, galaxies with higher $D_n4000$ have larger velocity
dispersions and smaller sizes. $D_n4000$ is a proxy for stellar population age,
thus these trends suggest that older galaxies typically have larger velocity
dispersions and smaller sizes. We combine velocity dispersion and size into a
dynamical mass estimator, $\sigma^2 R$. At a fixed stellar mass, $\sigma^2 R$
depends on $D_n4000$. The S\'ersic index is also correlated with $D_n4000$. The
dependence of $\sigma^2 R$ and S\'ersic index on $D_n4000$ suggests that
quiescent galaxies are not structurally homologous systems. We derive an
empirical correction for non-homology which is consistent with the analytical
correction derived from the virial theorem. After accounting for non-homologous
galactic structure, we measure $M_\ast \propto M_d^{0.998 \pm 0.004}$ where
$M_\ast$ is the stellar mass and $M_d$ is the dynamical mass derived from the
velocity dispersion and size; stellar mass is directly proportional to
dynamical mass. Quiescent galaxies appear to be in approximate virial
equilibrium and deviations of the fundamental plane parameters from the
expected virial relation may result from mass-to-light ratio variations,
selection effects and the non-homology of quiescent galaxies. We infer the
redshift evolution of velocity dispersion and size for galaxies in our sample
assuming purely passive evolution. The inferred evolution is inconsistent with
direct measurements at higher redshifts. Thus quiescent galaxies do not
passively evolve. Quiescent galaxies have properties consistent with standard
galaxy formation in $\Lambda$CDM. They form at different epochs and evolve
modestly increasing their size, velocity dispersion and S\'ersic index after
they cease star formation.
