The year in men’s tennis wraps up this week, with the top eight players still healthy enough after the long, long season, to compete in the round-robin A.T.P. World Tour Finals, which takes place every November. Since 2009, the tournament has been held at the cavernous O2 arena, in London, the kind of place you’d go to see aging rock veterans like the Stones or Springsteen. There’s something apt about this: men’s tennis has lately become no country for young men. In 1992, the average age of a top-ten men’s player was twenty-three; at the end of last year, it was roughly twenty-nine. It is true, though, that, for the first time since 2001, neither the thirty-five-year-old Roger Federer nor the thirty-year-old Rafael Nadal will be competing: knee troubles (Fed) and wrist troubles (Rafa) kept them off the court for long stretches this season, sending them down the rankings and out of the season finale. And so the story of this year’s tournament is shaping up to be whether Novak Djokovic, who has won the past four Tour Finals, can somehow summon his early-season form and regain the No. 1 ranking that, earlier this month, was seized, barely, by Andy Murray, who has been playing the best tennis of his career. (Djokovic had held the top spot since July of 2014, the fourth-longest streak in the history of the men’s game.) Both Murray and Djokovic will turn thirty in May. Twenty years ago, there was exactly one player who was thirty or older (Stefan Edberg) in the top twenty.

Perhaps in an effort to assure tennis fans that there is, in fact, a rising generation of men’s players, the A.T.P. has announced that, next November, a week before the Tour Final, in London, it will hold the first under-twenty-one Masters tournament, in Milan. The seven best youths on the tour, decided by ranking points, will be joined by the best young player from Italy, who will be given a wild-card entry by the tournament’s organizers. The format will be round-robin, and the hope is to have prize money in the neighborhood of $1.5 million—a fortune for tennis striplings. Almost all the best players under twenty-one spend the bulk of their time on the Challenger tour, the second tier of men’s pro tennis, where prize money is modest—typically fifty to seventy-five thousand dollars for a tourney—and as often as not the winners are veteran players ranked outside the top fifty, who are hungry for cash and ranking points. Attendance at these tournaments is scant, and network-TV cameras are nowhere to be found. (Some matches are streamed online.) If you’ve seen a teen-ager compete in a men’s game lately, it was likely on an outer court at Flushing Meadows, in the week before the official start of the U.S. Open. In these qualifying matches, players ranked far from the top twenty fight to win spots in the main draw, and some of them are youngsters. Other than an occasional early-round match at one of the majors, these “qualies” have, in recent years, offered fans of tennis their only chances to glimpse the game’s future.

I’m hoping that the new under-twenty-one event can begin to change that. Among the satisfactions of being a sports fan, is there anything more engaging than watching a young talent emerge, sharpen, and mature? It’s a pleasure that has not been available in men’s tennis for some time. Can you name the players younger than twenty-one in the Top 100? There are only five—one of whom, Russia’s Karen Khachanov, will be too old, come next fall, to make the cut in Milan.

Fans of a certain age can remember when teen-age players would burst onto the scene and quickly captivate audiences at major tournaments. There was John McEnroe, eighteen and punk-pale, his Fila shorts very short, his hair barely contained by a headband, serving, volleying, yelling, and racquet-kicking his way through the qualifying rounds and then the first week of the 1977 Championships at Wimbledon, before losing his semi-final match to Jimmy Connors. Mats Wilander won the French Open and the Australian Open as a teen-ager; Boris Becker won Wimbledon twice before he turned twenty. No teen-ager in the men’s game has got our attention like that since the spring of 2005, when Nadal made it to the finals of big tournaments in Monte Carlo and Rome and then, having just turned nineteen, won the French Open.

Men’s tennis has become an older man’s game, and it’s not only because a handful of players—Nadal, Federer, Djokovic, and Murray—have dominated with a greatness that seemed, at least until this year, to defy the passage of time. There are more fundamental reasons. The strength and resilience demanded by the power-baseline game and the gruelling, globe-hopping A.T.P. tour have a way of grinding down an adolescent newbie. He must spend years muscling up, quickening his lateral movement, honing his return game—which has become crucial in men’s tennis—and figuring out how to avoid being worn out or broken by the long rallies and the travel. Think of Kei Nishikori and Milos Raonic, who developed slowly, fought injuries, and took until their mid-twenties to climb into the top ranks. (They both qualified to play in this year’s Tour Final.) Austria’s Dominic Thiem, whom I wrote about in June, broke into the top ten this year and is playing in London this week. He’s twenty-three—by today’s standards, a wunderkind.

If the under-twenty-one tour final had been inaugurated this year, what would it tell us about the next generation of men’s stars? For one thing, it would tell us, surprisingly, that none are likely to be Spanish. Spain has ruled men’s tennis for the past decade, sending Nadal to confound Federer and become No. 1, placing four players in the top twenty in many years, and dominating Davis Cup play. But the most promising Spanish teen is the nineteen-year-old Jaume Munair, whose current A.T.P. ranking is No. 306, far from the under-twenty-one top eight. Meanwhile, it appears that the Russians are coming: in addition to Khachanov, who ended the year ranked No. 52, another young Russian, the nineteen-year-old Andrey Rublev, has been playing some fine tennis. The South Koreans are rising, too. That nation, which has never been a factor in men’s tennis, has two players who could have made this year’s cut, Hyeon Chung and Duckhee Lee. Lee is only eighteen, and will surely be one of the stories of the tournament if he qualifies next year. He was born deaf, and must rely on hand gestures from line judges and the chair umpire.

Three of the eight highest-ranked under-twenty-ones were Americans—perhaps, just perhaps, a sign that the United States, after a generation-long drought, might once again have a player or two in the top five. Jared Donaldson (age: twenty; ranking: No. 109) got the attention of the tennis world at the U. S. Open: after qualifying, he upset David Goffin, who was ranked twelfth, and beat Viktor Troicki before losing to Ivo Karlovic in the third round. Frances Tiafoe (age: eighteen; ranking: No. 108), in his second year as a pro, broke into the Top 100 for a while with a string of five appearances in the Challenger finals, two of which he won—and he played a gruelling, enthralling first-round match at the U.S. Open against the American veteran John Isner, taking the first two sets before eventually losing in a fifth-set tiebreaker. And then there’s Taylor Fritz (age: nineteen; ranking: No. 70), with his height (six feet four), his serve (a hundred and thirty-plus miles per hour), and his run, in February, to the final of the Memphis Open. He was the youngest American to reach an A.T.P. tournament semifinal since Michael Chang, in 1989. He lost, to Nishikori, but later in the month he got to the quarterfinals of the Acapulco Open and cracked the Top 100.