It wasn’t long ago that men’s tennis was known as “a young-man sport,” with most of the top players in the world under the age of 25 dominating the rankings. An ATP player approaching his late 20s was often considered “over the hill” as the young upstarts flourished in Grand Slam events and were saturating the top rankings.

Teenagers were winning majors, with Boris Becker taking Wimbledon by storm in 1985 as a 17-year-old, and Michael Chang also stunning the tennis world as a 17-year-old French Open champion in 1989. The trend would continue as Pete Sampras would win the U.S. Open at 19 in 1990, and 10 years later Marat Safin would win at Flushing Meadows at age 20 while Lleyton Hewitt would win it the following year, also at age 20. On his 19th birthday, Rafael Nadal defeated Roger Federer in 2005 to reach the French Open final, where he would go on to win the first Grand Slam of his career.

Youth dominance wasn't a new phenomenon at all. Young players  winning majors goes back to Ken Rosewall winning the Australian Open at age 18 in 1953, and continued with Bjorn Borg winning the French Open in 1974, just 10 days after turning 18.

But the days of youngsters dominating tennis seem to be over. The last time a Grand Slam winner was under the age of 21 was in 2009, when Juan Martin del Potro won the U.S. Open just days before his 21st birthday.

The current crop of elite tennis players is older even as the sport has become more physically demanding. It seems that not only are top players’ not slowing down, they may actually be getting better with age. It seems implausible for a relative newcomer to knock Novak Djokovic off his No. 1 ranking anytime soon, and the Serbian superstar turned 28 just last week.

In the current ATP Rankings, the average age for the Top 20 is 28.6 years old. That’s a sharp rise from the end-of-year rankings in 2004, when the average age of was 25.5.

At the moment, there isn’t one Top 20 player under the age of 24. Only Kei Nishikori is under the age of 28 amongst Top 5 players. Djokovic (28), Federer (33), Andy Murray (28), Tomas Berdych (29), Nadal (28), David Ferrer (33) and Stan Wawrinka (30) are proving that aging tennis stars are overall too tough for young players to handle. The youngest player in the Top 20 is Grigor Dimitrov, who turned 24 years old just 10 days ago.

A decade ago, a 23-year-old Federer was holding off top-ranked players like Andy Roddick (22), Hewitt (23), and Safin (24). There were also upstarts like Guillermo Coria (22), David Nalbandian (22) and Joachim Johansson (22), Tommy Robredo (22) and Mikhail Youzhny (22) battling in the Top 20.

Bruce Foxworth, a former tour pro living in Los Angeles who coached former stars Lori McNeil and Roger Smith, credits improvements to tennis rackets and strings, changes to player preparation, and new training methods, for the improved longevity of top players. But he also feels that the game is not lacking for athleticism with older players dominating.

“The athleticism is at a maximum,” said Foxworth. “The physicality of the game is at its peak, and guys are stronger. You got 6’4 and 6’8 guys moving around the court much better, and playing an all-around game.”

Foxworth credits certain players over 30 like Federer for not being “grinders” and therefore adding years to their careers. It’s a reason why Foxworth believes Federer was able to outlast stars like Hewitt, who was known for his scrappy play. In Federer’s current style, Foxworth points out that the Swiss legend is still able to approach the net and therefore effectively shortens points. His lengthy experience also provides him with such an all-around and refined game that he can still hold off most young challengers.

“It’s not like Federer is coming to the net with kamikaze desperation. He’s skillfully coming to the net,” said Foxworth.

An effective net game to shorten points is a good way for players like Federer to avoid being worn out due to long rallies. And even when matches extend beyond three sets, well-conditioned players like Federer still have their stamina against young players and have grown smarter in avoiding being burned out running along the baseline.

The state of tennis isn’t completely slanted towards players in their mid and late 20s. On Tuesday, 22-year-old Jack Sock upset Dimitrov in straight sets. Foxworth believes Sock has the potential to mature into an elite player. Meanwhile, Nick Kyrgios, 20, ranked No. 30, and Dominic Thiem, 21, ranked No. 31, are two other rising stars who have shown promise in recent months.

There were seven teenagers in the main draw at Roland Garros this year, yet 18-year-old Borna Coric, who is ranked No. 46, is the only one in the Top 50. He defeated Sam Querry in four sets on Monday, while 19-year-old Thanasi Kokkinakisa advanced to the second round to face Bernard Tomic.

But there still seems to be a shortage of young phenoms ready to burst on the tennis scene and seriously challenge Djokovic, Federer, Nadal and Murray in a Grand Slam. Coric defeated Murray in Dubai earlier this year, but when he faced Federer in the semifinals, he was trounced 6-2 6-1.

Indeed, it doesn’t seem wise to bet on a young challenger to put in a Chang-like performance at Roland Garros in 2015. Of all the top contenders in the tournament, only Kyrgios is under 24 years old, and he’s a 40-1 longshot.