  The epoch of galaxy formation provides an important additional test of
cosmological theories. Cold-dark-matter (CDM) models with cosmological constant
($\Lambda$) are designed to account for the observed excess power in galaxy
distribution, but at the same time suppress the power on small scales pushing
galaxy formation to recent epochs. We point out that the recently discovered
high redshift galaxy, 53W091, with accurate age measurements (Dunlop et al
1996) provides a particularly important test of these models. In the flat
$\Lambda$-dominated Universe, the redshift of formation of 53W091 decreases
with decreasing $\Omega$. However, in the modified CDM models decreasing
$\Omega$ suppresses the small scale power in the density field and this effect
turns out to be dominant. We estimate the mass of the galaxy and show that it
represents a very rare and unlikely event in the density field of such models.
Similar problems would occur in other modifications of the CDM cosmogonies.
