Mean stellar velocity dispersion (σ_*) measured at a galactocentric radius of 0.25−0.30 R₂₅ in the disk environment of all our sample galaxies for stellar populations with luminosity-weighted ages within the three different age bins defined in the main text. We note that for visualization purposes, the x-axis position of each data point is located at the edge of the age bin it represents. In each panel, the leftmost triangle represents the mean (area-weighted) velocity dispersion of all populations younger than 100 Myr. The central square marks the mean velocity dispersion of populations with 100 Myr < LumW age < 300 Myr, and the rightmost triangle shows the same quantity for populations older than 3 Gyr. The errorbar indicates the standard deviation of the σ_* values of the pixels within a given age bin. The bottom right panel shows the trend for all galaxies, colored by total stellar mass.