1-2 years.
Lee and Ayoub are the most promising kids of Juvenil A. Though not that much talent in our current Juvenil A. Onana his development over the last 3/4 months is pretty impressive. Best GK of this season in La Masia by some distance. Very allround. And there are some defenders like Quinti, Rodri, Juanma and Adria who are highly rated by most of the La Masia insiders... Don't agree fully. Quinti is perfect with the ball on his feet, but a poor man marker. Other 3 are better defenders, but not high-class quality imo.
EDIT: Not forget to mention some of the wonder kids of Juvenil B: Carles Aleña en Carles Pérez will run easily into the Barca B in 2 years time.
Correct me if I'm wrong but I heard the 2002 crop is more talented.
2001 > 2002.
Both generations are highly rated, but quality of 2001 is impeccable with Adria Bernabe, Nico, Ansu, Take, Eric. But important to keep in mind that Nico and Ansu are 2002 born, but play for 2001. The 2002 generation has some special kids with Pablo Moreno, Robert Navarro and Marc Domenech... has to be said that Pablo Moreno is playing with 2001 kids since Ansu's ban.