He abundance (upper panel) and age (lower panel) as a function of [Fe/H] for the relative (black lines) and absolute (red lines) approaches, using PGPUC (solid lines) and VR (dashed lines) models. These calculations use [α/Fe]= + 0.4. The assumed [Fe/H] value of V69 is depicted as a dash-dotted blue line. The errors for each Y and age estimation are not included, as they are discussed in Sect. 4.5.