We discuss three methods to estimate the age distribution of central
stars of planetary nebulae (CSPN) and their progenitor stars. These
methods include the use of an age-metallicity relation that also
depends on the galactocentric distance, an age-metallicity
relation for the Galactic disk, and the determination of ages from the
central star masses obtained from the observed nitrogen abundances. We
conclude that most CSPN in the Galactic disk have ages under 6 Gyr, and
their age distribution is peaked around 2-4 Gyr. These results
have been successfully compared with the age distributions of white
dwarf stars based on their mass distribution, and on available mass
determinations of CSPN.