(a) Systematic error, as a function of stellar population age and metallicity, introduced in horizontal branch based ages by a systematic error of 0.01 M_⊙ in the red giant branch mass loss. (b) Red giant branch mass loss relation of Savino et al. (2019, black solid line and red shaded band), adopted in this paper, alongside the relations of Gratton et al. (2010, blue) and Origlia et al. (2014, green). The band width represents mass loss uncertainties.