Sheboygan, Wis. ? The only number that matters at the PGA Championship is on the scorecard, not the birth certificate.

Nick Watney flips his club after missing a birdie putt on the 17th hole during the third round of the PGA Championship. Watney took a three-shot lead Saturday in Sheboygan, Wis.

Golf has been trending toward youth over the past several years, and on a Saturday at Whistling Straits, the final major of the year turned out to be a showcase of the next generation.

Leading the way was Nick Watney, whose college friends called him “Rube” after a character in “Major League II” because he was so polite to the seniors. He showed no mercy to Whistling Straits by firing off five birdies in the opening seven holes, leading the 29-year-old American to a 6-under 66 and a three-shot lead.

Right behind were 26-year-old Dustin Johnson and 21-year-old Rory McIlroy, two of the most talented young players on either side of the Atlantic. Both of them left their marks in the majors already this year, Johnson as the 54-hole leader in the U.S. Open, McIlroy for tying a record with a 63 at St. Andrews in the opening round of the British Open.

Of the top six on the leaderboard — five of those players in their 20s — none has won a major. The last time the top six contenders were this green in the PGA Championship was in 1992 at Bellerive, which Nick Price won for the first of his three majors.

“There’s some really good players that haven’t won a major,” Watney said. “And all the guys that have, at one point they hadn’t won, either. So you’ve got to start somewhere. And hopefully, tomorrow will be my day.”

Watney only seriously struggled at the end, when he went from deep rough on the right of the 18th to deep rough in the side of a hill left of the green. He did well to make a bogey and finish three long days at 13-under 203.

Johnson found enough accuracy to go with his awesome power for a 67, giving him a shot at redemption. He had a three-shot lead at the U.S. Open, only to lose it all on the second hole on his way to an 82.

He figures that will only help him.

“Any time you can be in that situation and know what to expect, you’ve definitely got a leg up on the other people,” Johnson said. “Because not everyone has been in that situation of being in the lead in a major. So I’m pretty confident. And I’ve been playing really well this week. I’m looking forward going into tomorrow.”

McIlroy also had a 67 while playing with Johnson, and while he made six birdies, he saved his round with a number of par putts from the 6-foot range that could easily have dropped him down the leaderboard.

McIlroy, who won the Quail Hollow Championship this year by closing with a 62, is coming off a memorable major of his own. He opened with a 63 at St. Andrews, got knocked sideways in the wind with an 80 in the second round, and rallied to tie for third.

Is he ready at age 21 to become the youngest major champion since John McDermott was 20 when he won the 1911 U.S. Open?

What’s too young anymore?

“The players are just getting so much better at a younger age,” McIlroy said. “Their confidence is so high that they can take on shots that other guys just might not have thought they could. I don’t know if that’s because most of the guys swing it better out here now or whatever, but it does seem the younger guys are coming out and they’re just a lot better and more ready to win.”

And there are a lot of them, especially at Whistling Straits.

Jason Day, the 22-year-old Australian who won in Dallas this year, had a 66 and was in the group at 9-under 207 that included Martin Kaymer, the 25-year-old from Germany who has top 10s in the last two majors. Kaymer shot 67.

The only player among the top six not in his 20s was the biggest surprise of all — Liang Wenchong, a 32-year-old from China who set the course record at Whistling Straits with a 64. He didn’t start playing the game until he was 15.

Some of these guys already were dreaming of winning majors at that age.

As for Tiger Woods? His only hope is to shoot his best round of his strange season today and try to earn a Ryder Cup berth.

Woods scrambled brilliantly in the morning to finish off the second round with a 70 and get within five shots, then opened the third round by stuffing his first couple of iron shots. He couldn’t make a birdie, however, and had to rally for a 72 on a day when the average score was 71 in soft conditions and relative calm.

Woods wound up 10 shots behind. He likely will need to finish at least in seventh place alone to make the Ryder Cup team.

“I just want to play a good round and see where that puts me,” Woods said.

Five of the last six major champions had never won one before, the exception Phil Mickelson this year at the Masters. To see so much inexperience at the top — not to mention youth — is not nearly as surprising in a year in which 27-year-old Louis Oosthuizen won the British Open at St. Andrews, and 30-year-old Graeme McDowell of Northern Ireland won at Pebble Beach.