Carvajal and Varane are 21 and 20 respectively.
The most promising young RB and CB in the world. (Ages 18-23)
Isco and Illarramendi are 21 and 23 Respectively.
The most promising playing of his kind along with gotze, and illarramendi, THE most promising player of his kind along with Gundogan. (not too many players with the kind of skill set of illarramendi).
Carvajal, Isco, Varane, Illarramendi, and Possibly Kondogbia.
21,21,20,23,20.
You have a decades worth of football there.
Jese and Morata are among the most promising in spain of their kind as well. 20 and 21 respectively.
All of the spanish talent mentioned could very well become staples in the Spanish NT in the future.