  High precision photometry as performed by the CoRoT and Kepler satellites
on-board instruments has allowed to detect stellar oscillations over the whole
HR diagram. Oscillation frequencies are closely related to stellar interior
properties via the density and sound speed profiles, themselves tightly linked
with the mass and evolutionary state of stars. Seismic diagnostics performed on
stellar internal structure models allow to infer the age and mass of
oscillating stars. The accuracy and precision of the age determination depend
both on the goodness of the observational parameters (seismic and classical)
and on our ability to model a given star properly. They therefore suffer from
any misunderstanding of the physical processes at work inside stars (as
microscopic physics, transport processes...). In this paper, we recall some
seismic diagnostics of stellar age and we illustrate their efficiency in
age-dating the CoRoT target HD 52265.
