Results. The number density of quiescent galaxies is found to increase since z similar to 1, with a more substantial variation at lower stellar mass. Quiescent galaxies feature extinction AV < 0.6, with median values in the range A(V) = 0.15-0.3. At increasing stellar mass, quiescent galaxies are older and more metal rich since z similar to 1. A detailed analysis of the PDFs reveals that the evolution of quiescent galaxies is not compatible with passive evolution and a slight decrease of 0.1-0.2 dex is hinted at median metallicity. The intrinsic dispersion of the age and metallicity PDFs show a dependence on stellar mass and/or redshift. These results are consistent with both sets of SSP models and assumptions of alternative star formation histories explored. Consequently, the quiescent population must undergo an evolutive pathway including mergers and/or remnants of star formation to reconcile the observed trends, where the "progenitor" bias should also be taken into account.