I have no problem with a teenage boy drinking on Purim in in parent’s presence, and I probably will allow my sons to drink, even to inebriation when they get old enough. I plan however on supervising it. But there is no way a yeshiva can truly vouchsafe the saftey of a bunch of rowdy drunken boys. All that’s needed is for one boy to be sick while asleep on his back, for a fatality to occur. Moreover, many boys go out to schnor while drunk, and the risk of traffic accidents is high.
Personally, I follow the Rema’s recomondation on Purim.