For generations, the baseball all-star game was actually about teams made up entirely of certified stars. In 21 seasons, Hank Aaron was an all-star. Willie Mays and Stan Musial made those teams 20 times apiece, and Cal Ripken Jr. did it 19 times. They are the standard-bearers.

But for decades, repeaters were so common you almost felt you could name next season’s team as easily as this year’s. In all, 62 players were all-stars in at least 10 seasons. As a result, this glamorized exhibition created a worshipful reverence for household names, though the game flirted with calcification at times. Often, this showcase was about bittersweet goodbyes.

This time, the only “goodbye” is to the all-star game as we remember it.

Just 11 of the 34 members of the National League club here have been on more all-star teams than 20-year-old Bryce Harper of the Nationals. Harper has been an all-star twice. So has Mike Trout, 21, of the Angels. Yet vet Brandon Phillips says, “Trout is the best all-around player in the game.” Many would say the best is Miguel Cabrera. But the point is that kids, and players who were barely known until this year, are now in the debate.

Exactly half of the 68 players here are in the same boat as the Orioles’ Chris Davis and Manny Machado of the American League: first-timers. Counting those, like the Nats’ Jordan Zimmermann, who are all-stars but can’t play because of injuries, this year has produced 39 first-time all-stars. But that doesn’t keep some of them from being discussed in historic terms.

The Post Sports Live crew debates whether Bryce Harper will have a more exciting appearance in the MLB All-Star Game or in the Home Run Derby. (Post Sports Live)

“Davis is having an historic type of year,” J.J. Hardy said of his teammate who is on pace for 62 homers, which some, including Davis himself, would consider a “clean” homer record. “In batting practice we have a three-swings, longest-ball contest. Chris only hits his to the opposite field, and he still always wins. He does it just to embarrass us.”

Just one man in this entire celebration has been on at least 10 all-star teams: Mariano Rivera with 13. David Ortiz is runner-up with nine, a total that puts him in a 19-way tie for 63rd place.

This all-star game of infants and toddlers is not bad. It’s just stunning.

With a generation of dazzling physical talents arriving, the 2013 All-Star Game is actually about making introductions.

Hello, there. Who are you? And are you as amazing as everybody says?

Teams such as the Nats and Orioles are in the middle of it with the kind of young talent that is redefining the new limits of the old sport, and doing it in an era when baseball may have the best — or least lousy — drug-testing in major American sports.

In recent years, a PED-inflated generation has been shoved toward the exits, their departures often almost surreptitious, with precious few midsummer curtain calls for aged, suspect 500-homers guys. Gentlemen such as Alex Rodriguez and Ryan Braun are conspicuous by their absence, though lengthy PED suspensions may await them, and possibly 20 big leaguers in all, as a result of MLB’s Biogenesis investigation.

The Post Sports Live crew debates whether shortstop Ian Desmond is the Nationals’ MVP up to this point in the season. (Post Sports Live)

Baseball has seen changing of the guards and new waves and talent infusions in the past. But it may never have seen anything like what is being celebrated on Tuesday night here at Citi Field. What is on display verges on being a new form of the sport.

“The young pitching is better than it’s ever been. That what impresses me the most of anything in the sport,” NL shortstop Troy Tulowitzki said. “Starters throw in the mid-90s and relievers even harder. They’re the best arms the game has ever seen.”

Fastballs are faster now, with 95 mph almost commonplace. The Nats just used Class AA call-ups Nathan Karns and Taylor Jordan who touched 97 and aren’t even considered unusual. Even 100 mph is not so unheard of, especially for NL starter Matt “The Dark Knight of Gotham” Harvey.

“Matt throws 100, has a cutter, a knuckle-curve, a slider, a change-up. He throws everything,” Harper said. “He’s one of the best pitchers in the game right now, if not the best. Maybe I’m going crazy but he could be one of the best pitchers of all time.”

One Reds reliever here, Aroldis Chapman, was clocked in his last game at 105. Few even mention Stephen Strasburg’s speed any more though he’s still second among starters to Harvey.

These days, if you face a hurler with a 96-mph heater, plus two other quality pitches and control, you are supposed to be able to cope. And such hitters, especially young ones with blurred bat speed and NFL-size frames, seem to have arrived just in time to deal with it. The 225-pound Trout, who looks like he dropped out of the WWE’s “Monday Night Raw,” as well as the 230-pound Harper and Machado, are already building their legends.

Last week Machado made a 160-foot throw to first base while falling down backward that Brooks Robinson would’ve needed a cutoff man to duplicate. The Cards’ Adam Wainwright didn’t seem to want to talk about anything else at his media sessions.

“Manny made it look like the game was in slow-motion for him. He threw it with no [forward] momentum,” Hardy said. “I saw it and said, ‘Is this kid for real?’ Unbelievable.”

Perhaps the best of this barely believable breed isn’t even here because, somehow, some dolt forgot to invite the one player that everybody in baseball wants to see: the Dodgers’ 245-pound Yasiel Puig. The rookie may be the fiercest combination of opposite-field power, all-fields-average hitting, Cuban bravado and just-plain-stupid warp speed that baseball’s seen.

International arms inspectors are alerted when he unleashes throws from right field. He’s hitting .391. Of course, because this is baseball, there may be holes in his swing that haven’t been found yet, and he’ll end up back in Class AAA. Don’t bet on it. Puig, invisible here, comes to Nats Park this weekend.

The sentimental highlight of Tuesday night has already been determined.

“It would probably be the most beautiful touch in the world if we could somehow get a lead and play the ninth with the greatest closer of all time coming out of the bullpen,” said AL Manager Jim Leyland, aware that seven of the last nine World Series have been won by the team with home-field advantage, the prize that’s determined by winning this game.

“But we need to get that lead first,” Leyland added. “Rest assured, one way or the other, you will see Number 42 pitch.”

Mo’s moment is predictable. What makes this year’s All-Star Game so promising, and baseball in general so healthy, is that you have little idea what the sport’s greatest players, especially the young ones, will do these days. Some, like Harvey on what may be a 100-mph first pitch of the first inning to Trout, seem determined to perform on a scale the game has never seen.

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