Joining a Nationals team that already has a top youthful star in ace pitcher Stephen Strasburg, Harper has a .282 batting average with eight homers and 25 RBIs in 63 games. The only younger All-Stars were Bob Feller in 1938 and Dwight Gooden in 1984, both closer to their 19th birthdays than Harper.
"I still feel like I have that kid inside me that wants to play the game of baseball every single day," Harper said. "I got love and that passion for the game and, hopefully, I can keep it going. I hope I'll be able to play for the Nationals for a long time and be able to play in the big leagues for a long time because that's the dream."
While Harper is polished following years of interviews, Trout projects a golly-gee demeanor, with close-cropped hair and a beaming smile. After he twice crashed into the center-field fence at Denver's Coors Field last month, teammates Jered Weaver and Dan Haren suggested he turn down the enthusiasm a few notches.
"'It's a long year. We're going to need you,'" Trout remembered them telling him.
He's hitting .341 with 12 homers, 40 RBIs and 26 steals in 29 chances.
"I was just telling Jete, I've never seen a player hit a triple to left field, down the line," Yankees ace CC Sabathia said. "Raul (Ibanez) plays it off the wall, and he's standing on third. That's just fun to see. What he's doing is amazing."
While Trout was an All-Star shoo-in, La Russa appeared reluctant to select Harper and added him on Saturday as a replacement when Miami's Giancarlo Stanton got hurt.
Even the 67-year-old La Russa, who managed his first World Series champions before Trout and Harper were born, appreciates the focus on the new stars.
"It would be nice to put the National League phenom against the American League phenom," he said.
When discussing Trout, Harper sounds like a fan.
"He's fun to watch. I get pumped to watch him," Harper said.
They hope this is just the first of many All-Star appearances. For every Willie Mays, who played his 24th and final All-Star game in Kansas City, there is a Gooden, who was selected in four of his first five seasons and then flamed out because of injuries and drug use.
Harper and Trout know what they can become. They are the next generation, playing alongside the present.
"I think certain guys who have been introduced to the game of baseball early on in life," said 40-year-old Chipper Jones, who is retiring at the end of the season. "Travel ball has accelerated so much for the development of young players these days. Back when I played, we played 30 games a year, and I'd move on to football and basketball, and run a little track."
Yes, much has changed. But much is the same.
Harper wants to become just like Jones, a perennial All-Star respected by his peers.
"Any time I can do that and be that guy that's the face of baseball, I think that would be great, to be able to do that, to be able to play the game for a long time and respect everybody around me and respect the league," he said. "That would be a lot of fun."
NOTES: Detroit's Prince Fielder became only the second player to win multiple titles in the Home Run Derby, thrilling a crowd of 40,351 with eight splash shots into the right-field fountain and beating Toronto's Jose Bautista 12-7 in the final round. Ken Griffey Jr. won it three times.
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