Dynamical age t_dyn (Eq. (3)) as a function of the real evolutionary time t_evol for the basic model. Dashed lines are calculated from sizes and velocities taken directly from models, and solid lines are solutions derived from angular sizes and velocity extents corresponding to methods used in the Milky Way. Red colour is the model without the external gravitational potential (e.g. without the galactic shear). Black and blue lines correspond to the same model but viewed, at each time t_evol, at a specified position in the Milky Way: at l = 244° (black) and at l = 116° (blue, symmetrically around the anticenter line). The grey dotted line is the analytical solution (Weaver et al. 1977).