The evolutionary stage of a powerful radio source originated by an AGN is related to its linear size. In this context, compact symmetric objects (CSOs), which are powerful and intrinsically small (< 1 kpc) radio sources with a convex synchrotron radio spectrum that peaks around the GHz regime, should represent a young stage in the individual radio source life. Their radio jets expand within the dense and inhomogeneous interstellar medium of the host galaxy, which may influence the source growth. The radio emission is expected to evolve as a consequence of adiabatic expansion and radiative and inverse Compton losses. The role played by the different mechanisms in the radio and gamma regimes is discussed.
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