  The age of the Universe at a given redshift is a fundamental relationship in
cosmology. For many years, the uncertainties in it were dauntingly large, close
to a factor of 2. In this age of precision cosmology, they are now at the
percent level and dominated by the uncertainty in the Hubble constant. The
uncertainties due to the parameters that describe the current cosmological
model, $\Lambda$CDM, are much less important. In decreasing order they are:
uncertainty due to the matter density $\Omega_M$ around 0.9\% for $z> 3$;
uncertainty due to the dark energy equation-of-state parameter $w$, less than
0.3\% for $z>3$; and uncertainty due to the curvature parameter $\Omega_k$, at
most 0.07\%.
