Federer can easily go to his mid thirties playing at very high level. Nadal will play into his thirties against all reasoning. Don't know if Djokovic has the commitment of those two but he could go into his thirties no problem. Even with the slowness of the courts and the amount of tournaments played, careers are going to go longer and longer a la Agassi. Oh yeah, and anyone who uses the term grandpa for late Agassi is talking garbage. I feel sorry for the younger generations. Their being stifled.