Evolution in time of the dispersion in the η′ coordinate for a simulated YLA with initial conditions IC-1 and following orbit-1 (from left to right) with ages of 20, 50, and 80 Myr (marked with a vertical black dashed line) with 1000 Monte Carlo realisations of the observational errors. The different lines are the intrinsic dispersion (σ_int, cyan dot-dashed line), the propagated observed dispersion for each Monte Carlo realisation (σ_obs, dark blue solid lines), the dispersion due to observational errors (σ_err, red lines), and the estimated intrinsic dispersion (σ_est, green solid lines). The light grey shaded region represents the uncertainty in the dynamical age determined with the propagated observed dispersion, and the dark grey shaded region represents the uncertainty in the dynamical age determined with the estimated dispersion.