Central stellar mass density Σ_{1 kpc} versus stellar mass (left) and versus age (right). Left − The surface stellar mass density Σ_{1 kpc} within 1 kpc radius is plotted as a function of the stellar mass of the galaxies. The different colors mark the different mean age of the stellar population of the galaxies resulting from the best fitting to their SED. The large colored triangles represent the median age in four bins of stellar mass. Right− The central stellar mass density of cluster and field elliptical galaxies at z ~ 1.3 is plotted as a function of the age of their stellar population. Symbols are colored as a function of stellar mass.Errorbars are not shown to highlight the relationship between the quantities.