Tomas Berdych, this year's Wimbledon runner-up, is making his debut at 25, while Federer is the oldest at 29 in his ninth straight appearance. Andy Roddick and David Ferrer are both 28, while Robin Soderling is 26 and top-ranked Rafael Nadal is 24 — and qualified for the sixth straight year.
"It's quite surprising for me, because when I was coming up there was (Lleyton) Hewitt and (Marat) Safin and Roddick and (Juan Carlos) Ferrero and Tommy Haas, they were all excellent players and in the top 100 as teenagers," Federer said. "It was normal, and on the women's side it was even more extreme.
"But maybe the game has become more physical and more mental, and that's why maybe players today need a bit more time to break through."
Indeed, many players seem to reach their potential in their mid-20s these days. Berdych had his breakthrough when he stunned Federer in the Wimbledon quarterfinals this year before losing to Nadal in his first Grand Slam final.
Soderling made a similar splash by beating Nadal at the 2009 French Open, before going down to Federer in the final. This year, he beat Federer in the quarterfinals before losing to Nadal in the title match.