Like Uncle Toni said last week, if the next gen doesn't show up soon, Federer will be playing (and winning) until he is 45. Based on this year's results, I don't see why Federer cannot compete for championships at the other 3 slams until he is 40. It all depends on Djokovic. If Novak wants to, he has enough time on his side to finish with the most career slams.