KISSIMMEE, Fla. — In a batting cage on a back field at the Houston Astros’ spring-training facility, Carlos Correa rocks back ever so slightly, lifts his arms as he strides forward, then whips his bat through the hitting zone with a smooth but furious uppercut and lashes ropes to the gaps. He looks equally polished taking infield practice, showing off the incredible baseball instincts that thrilled scouts even years before his big league debut, shuffling confidently and directly toward every grounder hit his way then rifling the ball across the infield with easy arm strength.

Then, while jogging over to another field for more practice, he stops to sign autographs, hug children, and pose for photos with babies. Only his body itself betrays his age: Correa is huge — 6’4″ and 210 pounds without even an inkling of baby fat — but still owns the lanky, limby type of frame associated with late adolescence, like an 11-month-old Great Dane already giant but clearly not yet fully filled out.

Correa is 21 years old and already perhaps the best shortstop in all of baseball. He entered 2015 without a single game above Class A ball on his professional resume, then played his way to the big leagues by early June and hit .279 with an .857 OPS and 22 home runs in 99 regular-season games, helping power the Astros to a surprise Wild Card berth. Houston beat the Yankees in the AL Wild Card game, and afterward Correa finally drank his first beer.

“I learned a lot, man,” Correa told USA TODAY Sports when asked about his first big-league season, which earned him an AL Rookie of the Year Award. “The most important thing I learned was how to work hard but smart, don’t overdo anything or get carried away. Sometimes I used to work really hard, then be tired by game time. That’s one of the things I learned at the big-league level, especially because you have 20 more games than in the minor leagues. When you’re competing to try to make the playoffs, the grind is real. The pressure is on. So it’s a lot tougher. But it was a pretty special year overall.”

“Special” might be an understatement: Breaking into the big leagues at Correa’s age and producing like he did while playing the game’s most difficult defensive position is exceptionally rare. In Major League history, only four shortstops have ever produced at least an .850 OPS in at least 250 at-bats at age 21 or younger: Correa, Hall of Famer Rogers Hornsby, Hall of Famer Arky Vaughn, and Alex Rodriguez.

“I don’t put limitations on him, in terms of what’s possible,” Astros manager A.J. Hinch said. “He has got a lot of talent. He has good makeup. He has tremendous drive. I think he can be as good as anyone expects.”

“For him to jump straight into the big leagues and do what he did is pretty impressive,” said teammate Jason Castro. “Obviously there’ll be some adjustments, the league will start to adjust to him a little bit and try to exploit what little weaknesses he does have, but I think what makes him special is that — we saw it even as last year progressed — the way he responds to those adjustments from around the league.

“He’s an impressive guy to watch, and I’m looking forward to see what he can do this year.”

Castro and Hinch both noted the on-field adjustments Correa will have to make in his second big-league season, but in a grander sense, it’s hard to imagine a 21-year-old seeming better adjusted to the superstardom looming in his immediate future. In the clubhouse, he maintains a loose, easy affability with his teammates, but turns measured and professional when faced with a tape recorder. After the Royals eliminated the Astros from the postseason — in an ALDS that saw Correa hit .350 with a 1.081 OPS — he even made a series of TV appearances from the World Series.

“For me, it’s not only about baseball,” Correa said. “I want to be able to be a great baseball player, but an even better human being. I think if I want to impact society in a positive way, like Roberto Clemente did, I’ve got to do all that kind of stuff. I’ve got to show my face out there, and get people to know me in order to be able to great things for different foundations and for different people, especially the kids.”

Correa was the youngest position player in the Major Leagues in 2015. He won’t turn 22 until September. His production and polish suggest the experience of a veteran player ten years his senior, but only a player of his age could boast such sky-high potential. Baseball fans have perhaps been spoiled in recent seasons by the precocious success of young stars like Mike Trout, Manny Machado and Bryce Harper, but even Trout struggled in his first brief turn through the Majors, and neither Machado nor Harper posted offensive numbers better than Correa’s rookie rates until last season. And none of those guys regularly plays the game’s most premium defensive position.

Correa’s first 99 games’ worth of big-league experience prove nothing, but they tease so much. He enters 2016 with a real chance of emerging as the game’s best all-around player, and everything at Astros camp suggests he’s ready for it.