De Rossi at the age of 21 and Gattuso at the age of 22 were already part of the Italy national team. Pirlo's case was different. At that moment, he was still considered as the heir of Roberto Baggio, playing as a mezzapunta/trequartista and was on loan from Inter in teams like Reggina and etc. But the fact he played for Inter of that moment is an important factor why he couldn't exploit.
Anyhow, all the three won the champion of the U-21 Euro (Pirlo and Gattuso won the 2000 U-21 Euro and De Rossi won the 2004 one), which at least showed that they were one of the best youngsters of their generation. Let's see how will the likes of Marchisio, De Ceglie and Giovinco do in the next year's U-21 Euro. I don't really think they can compare with the Italian generation of 74-79, who are simply too good.
As to the likes of Aquilani and Montolivo, I never see them as world-class. They are not and would never be, IMHO. I think the 86-87 generation of Marchisio, Cigarini and etc have the potential to become better, but not as good as Pirlo, Gattuso, De Rossi and etc.