I think only in the fast courts ie Wimbledon and the us open would we possible teenage winners because they haven't developed the overall consistency to grind out wins at the AO and FO. Those courts are just so hard to catch fire and blast winners all day.
Maybe in a few years when the top 4 are 29/30 someone could sneak one in, but I wouldn't bet on it. It's just too hard to stay hot for 2 weeks. Even Del Porto and Djokovic, both who won at 20, were hot yet established in my opinion.
The players are so consistent now and the futher you go, the more consistent they get. Even big hitters aren't as erratic as the previous generation of players. I don't blame the crop of young talent but rather the overwhelming quality of the guys at the top.