I've had great success with very young sides. I do generally have a few vetran players in the squad (kepper, MC, DC...) but lean heavily on youngsters.
I am inclined to believe that some of this is do to my approach. I play a counter attacking style with lots of through balls and EVERYONE has pace. (I also look for off the ball, work rate and stamina).
I build my squad (and tactics) around the dual American sports adages "Speed kills" and "Speed corrects a lot of mistakes."
I tend to overhaul every team I manage to incorporate my style. Why not start with young players...especially since they can be so much cheaper!