While watching Djokovic-Cilic tonight (and prompted a bit by the TV commentary), I started thinking about top male teenage players, or the lack thereof. So why are there none these days? There was Becker, Edberg, Wilander, McEnroe, Sampras who were elite players before they were 20. Why none now? Is it because with today's power game, you have to be physically mature enough to compete at that level consistently enough to be considered an elite player?