 Born in Brescia, Lombardy, Castellini joined made his professional debuts at U.S. Cremonese at only 17, going on to appear for the club in both the Serie B and Serie C1.In the 2000 summer he moved to Torino FC, achieving promotion to Serie A in his debut season whilst appearing in 33 games.From January 2004, Castellini served a loan at his hometown club, Brescia Calcio of Serie A – Torino had been again relegated – after which he was released by "Toro".