On September 14, 2009, Juan Martin del Potro beat Roger Federer in the fifth set of the U.S. Open final, claiming his first major title just days before his 21st birthday. In the Open era, only 12 men have claimed a Grand Slam title at a younger age, among them all-time Slam leaders Bjorn Borg (11 career titles) and Pete Sampras (14).
Tennis is a young man’s game. The records of Borg, Sampras, and slightly lesser lights such as Wilander and McEnroe suggest that to build a legacy of greatness, a player must lay the cornerstone at an age when he might be a college sophomore or junior.
But not necessarily. The game’s most accomplished title collector, Roger Federer, didn’t win his first major–Wimbledon in 2003–until he was almost 22. Agassi and Lendl started later still.