Verification of the method to assign a time limit to the merger from the age distributions of the galaxy components. Shown are the stellar age distributions of the disk, warm, bulge, and hot inner stellar halo components for TNG50 468590, TNG50 375073, TNG50 220596, and TNG50 2 from Panel (a) to Panel (d). In each panel, the left plot is the true stellar age distribution from the stellar particles in the simulation, the right plot is the distribution from our best fitting model, and the vertical dashed line marks the end of the last massive merger.