  The weak radio source LBDS 53W091 is associated with a very faint (R approx.
24.5) red (R-K approx. 5.8) galaxy. Long spectroscopic integrations with the W.
M. Keck telescope have provided an absorption-line redshift, z=1.552 +/- 0.002.
The galaxy has a rest frame ultraviolet spectrum very similar to that of an F6V
star, and a single-burst old stellar population that matches the IR colors, the
optical energy distribution and the spectral discontinuities has a minimum age
of 3.5 Gyr. We present detailed population synthesis analyses of the observed
spectrum in order to estimate the time since the last major epoch of star
formation. We discuss the discrepancies in these estimates resulting from using
different models, subjecting the UV spectrum of M32 to the same tests as a
measure of robustness of these techniques. The models most consistent with the
data tend to yield ages at z=1.55 of >3.5Gyr, similar to that inferred for the
intermediate-age population in M32. Depending upon the assumed Hubble constant
and the value of Omega_0, only certain cosmological expansion times are
consistent with the age of LBDS 53W091; in particular, for Omega_0=1, only
models with H_0 < 45 km/s/Mpc are permitted. For H_0=50 km/s/Mpc and
Omega_0=0.2, we derive a formation redshift, z_f >= 5.
