are denoted by the colors red and blue, respectively, while the grey points are the middle quartiles. The dotted line signifies the maximum age of the universe within each redshift bin. The bottom panels contain histograms of colors, where the red and blue dotted lines in the bottom panels are the median colors of the two quartiles and the black, dashed line is the median color over the entire redshift interval. The general trend at all redshifts is that redder galaxies are typically older than bluer quiescent galaxies.[]{data-label="agecolor"}](fig4_sm.eps)

Absolute ages may not be very meaningful given our modeling approach, but the relative ages of blue and red galaxies are robust if we assume that they have similar star formation histories. In Figure \[agecolor\], we plot the best-fit age of all quiescent galaxies as a function of their rest-frame $U$-$V$ color. The reddest galaxies have systematically older stellar populations than the bluest galaxies at all redshifts. Given the assumption of solar metallicity, there exist a few quiescent galaxies consistent with the age of the universe (dotted horizontal lines) at $z\!\gtrsim$1. We include the typical 68% confidence intervals in the ages in Figure \[agecolor\] from the modeling described in §2, rather than 