I don't want to hark on about the good old days when I was the boss, but I do think my policy on age was sound. I pciked all the 21 year olds I felt were good enough to play NT21 international ball and then the best 20 year old and 19 year old prospects so that I could closely follow their progress - the likes of Barnett Singleton and Mark Alexander. That waym you can have a dialogue with the players coach (If he'll talk to you) or at least have a better idea of what type of players you'll need to play alongside them and then talk to the coaches of the other 20 year olds, to see if they are receptive to training their player in a certain way in order to make the NT, or have a starting place next year rather than a spot on the bench.
But, when it comes to court time, the only benefit of playing young players is to assess how they perform - forget xp gains, they are tiny, tiny, tiny.