Zidane didnt move to Juve until he was 24, and he was hardly the world's most famous youngster back then. Davids, and Reiziger, for instance, were regarded as better "prospects". And nobody would have given him a chance at that stage of career that he would turn out to be better player than Del Piero, Raul, and Ronaldo, so called big 3 cant miss talents.
Morfeo, on the other hand, were tipped to become the next wunderkid by the age of 16, and expected to become equal player to Francesco and Totti. The matter of fact is that it is hard to predict the learning curve of a particular player, and thus different people mature at different age. Maresca isnt the youngest player around, but I do think he deserves a chance, given that he opportunities had been limited until now.