Are compact steep-spectrum sources young?

Compact Steep-spectrum Sources form a remarkable class of radio sources accounting for a substantial fraction of the extragalactic objects selected at radio frequencies. In this paper we discuss the possibility that the majority of them are Young Sources. We argue that, unless the physical properties of the external medium are much more abnormal than we expect, these objects are likely to have ages of typically 10^6^ years and are the precursors of larger size radio sources. We also argue that their luminosity must decrease by a factor ~10, as they evolve to extended radio sources and as their sizes grow from a few kpc up to hundreds of kpc.