  By means of a semi-analytic model of galaxy formation, we show how the local
observed relation between age and galactic stellar mass is affected by assuming
a DM power spectrum with a small-scale cutoff. We compare results obtained by
means of both a Lambda-cold dark matter (LambdaCDM) and a Lambda-warm dark
matter (LambdaWDM) power spectrum - suppressed with respect to the LambdaCDM at
scales below ~ 1 Mpc. We show that, within a LWDM cosmology with a thermal
relic particle mass of 0.75 keV, both the mass-weighted and the
luminosity-weighted age-mass relations are steeper than those obtained within a
LambdaCDM universe, in better agreement with the observed relations. Moreover,
both the observed differential and cumulative age distributions are better
reproduced within a LambdaWDM cosmology. In such a scenario, star formation
appears globally delayed with respect to the LambdaCDM, in particular in
low-mass galaxies. The difficulty of obtaining a full agreement between model
results and observations is to be ascribed to our present poor understanding of
baryonic physics.
