Position of MOA-2010-BLG-523S in the HR diagram. Two sets of isochrones from Demarque et al. (2004) are plotted with metallicities as indicated in the figure. For each set of isochrones the ages of 1, 5, 10, and 15 Gyr are shown. If the star is indeed an RS CVn star, its metallicity is probably too low by up to 0.1 dex, and its effective temperature is too low by a few hundred degrees, while its surface gravity is likely to be unchanged. As can be seen, that change has essentially no effect on its estimated age.