Empirical relation between the luminosity-weighted ages of mock galaxies made of random mixtures of two SSPs, Age_L,mock, and the best age determination for such mock galaxies derived from a single SSP fitting, Age_SSP. The yellow curve is the Age_L,mock median for a given value of Age_SSP, and it represents the typical offset in age that one may expect when interpreting the SED of a mixture of two SSPs by fitting a unique SSP.