Assessment of different sources of uncertainty on our ages. a) shows the correlation between σ(B − V) and σage. Here we choose σ(B − V) = 0.005, a typical value for our photometry. The resulting age uncertainty is generally small (≤ 1 Gyr) and increases from young, metal-rich, to old and metal-poor stars. In b) the effect of 0.12 mag variation in the distance modulus on the derived stellar ages is shown. For shorter distances, generally younger ages are obtained with an increasing effect for older stars. In c) the sensitivity of our age analysis on the assumption of stellar metallicity is shown. Similar to the photometric uncertainty, the effect increases with stellar age but is significantly larger for typical uncertainties of σ [Fe/H] = 0.1. Finally, d) shows the age sensitivity on the adopted [α/ Fe], relative to a solar ratio which reveals a very similar and only slightly smaller effect on stellar ages than σ [Fe/H].