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abstract: 'With a complete, mass-selected sample of quiescent galaxies from the NEWFIRM Medium-Band Survey (NMBS), we study the stellar populations of the oldest and most massive galaxies ($>$10$^{11}$ M$_{\odot}$) to high redshift. The sample includes 570 quiescent galaxies selected based on their extinction-corrected $U$-$V$ colors out to $z$=2.2, with accurate photometric redshifts, $\sigma_{z}$/(1+$z$)$\sim$2%, and rest-frame colors, $\sigma_{\mathrm{U-V}}\!\sim$0.06 mag. We measure an increase in the intrinsic scatter of the rest-frame $U$-$V$ colors of quiescent galaxies with redshift. This scatter in color arises from the spread in ages of the quiescent galaxies, where we see both relatively quiescent red, old galaxies and quiescent blue, younger galaxies towards higher redshift. The trends between color and age are consistent with the observed composite rest-frame spectral energy distributions (SEDs) of these galaxies. The composite SEDs of the reddest and bluest quiescent galaxies are fundamentally different, with remarkably well-defined 4000$\mathrm{\AA}$- and Balmer-breaks, respectively. Some of the quiescent galaxies may be up to 4 times older than the average age- and up to the age of the universe, if the assumption of solar metallicity is correct. By matching the scatter predicted by models that include growth of the red sequence by the transformation of blue galaxies 