Different age definitions and their relation to stellar mass on an example. The grey line represents the SFH of the galaxy while the grey shaded area is in the future of the observation (the “0” of the x-axis represents the formation of the galaxy). The blue and red areas represent one-quarter and half of the stellar mass, respectively. Finally, t_{M/ 4} and t_{M/ 2} show the time since the onset of the star formation and the time to build up 25% and 50% of the stellar mass, respectively. In this example the galaxy is observed 2.5 Gyr after the start of star formation, Gyr, and the stellar mass is 10¹⁰ ℳ_⊙. This induces Gyr, Gyr, and Gyr.