Propagating Gaia-Era Distance Errors Into Globular Cluster Ages

A turnoff age is only as good as the distance that converts apparent brightness into luminosity. The Gaia mission changed cluster distances from a patchwork of methods into a homogeneous, parallax-anchored scale, but homogeneous is not the same as exact. This study propagates representative Gaia-era distance-modulus uncertainties for six clusters through the turnoff age sensitivity. A modulus uncertainty of a few hundredths of a magnitude becomes an age uncertainty of 0.25 billion years in the best case, NGC 6397, and 0.63 billion years in the worst case studied, NGC 2808. Distance remains a leading term in the cluster age error budget even after Gaia, and claims of total age errors smaller than the distance term alone are not credible. Inputs are published distances and a stated isochrone sensitivity; the work is a propagation, not a new astrometric measurement.