Age-related quantities for the Galactic BNSs as discussed in Sect. 2: the characteristic age τ_c (brown, through Eq. (2) and the kinematic ages τ_kin assumming GC isotropy (dark green for χ₁ and light green for χ₂) and kinematic ages assuming LSR isotropy (dark purple for χ₁ and light purple for χ₂). The boxes extend from the first to third quartile (25% to 75% percentile) of the distributions, while the whiskers show the 5% and 95% percentiles and the different coloured lines show the medians. The figure also contains lines corresponding to τ_gw (dash-dotted lines), the Hubble time τ_H = 13.8 Gyr (dotted line, Komatsu et al. 2011), as well as a background line at t = 40 Myr (dashed line, relevant for Sect. 3). The median values of these distributions and their uncertainties are listed in Table 2. For J0737−3039A/B we show τ_c of J0737−3039B.