Left: standard 1σ envelope of the binary system age relative error in dependence on the mass of the primary star (solid black), compared with the same quantity obtained by sampling from the grid with a different initial helium abundance computed assuming ΔY/ ΔZ = 1 (dashed red) and ΔY/ ΔZ = 3 (dot dashed green). Middle: same as the left panel, but in dependence on the mass of the secondary star. Right: same as the left panel, but in dependence on the system mass ratio q.