Radial abundance gradients from planetary nebulae and young objects: Age effects

We discuss the effects on the time variation of the gradients resulting from our determinations of the age distributions of CSPN. The main conclusions are: (i) for most CSPN with accurate radial velocities the kinematic ages are usually under 3 Gyr, so that the differences between the gradients of these objects and of younger objects are expected to be small; (ii) results based on age-metallicity relations suggest that there is an older PN population for which the gradients are steeper, in agreement with open cluster data.