Upper panel: age distribution of stars formed during the whole Galactic history predicted by our two-infall chemical evolution models. Middle panel: age distribution of the observed high-α sequence stars of the VSA18 sample (purple histogram) compared to the predicted distribution of stars created during the first infall episode, and taking into account the errors given by Eqs. 10 and 11 (cyan histogram). Lower panel: age distribution of low-α stars in the VSA18 sample (green histogram) compared to the model-predicted distribution of stars created during the second infall episode, taking into account the errors given by Eqs. (10) and (11) (cyan histogram).