Carlos Correa was 20 years old when he played his first Major League game on June 8, 2015. He collected his first hit that night and went on to hit 22 home runs in 99 games with an .857 OPS that season. He was voted 2015 American League Rookie of the Year.
Remarkably, Correa never once looked overmatched in those 99 games, and partly because of him, the Astros made their first playoff appearance in a decade.
Six days after Correa's debut, Indians manager Terry Francona wrote 21-year-old Francisco Lindor's name on his lineup card for the first time. The Indians didn't make the playoffs in 2015, but will open the 2019 season having won the AL Central three years in a row.
In that time, Lindor has made the AL All-Star team every year and been a top 10 finisher in the MVP race. Like Correa, there was never a question about his belonging in the Major Leagues at such a young age. He did.

It's not just that teams are fast-tracking their best young players through the Minor Leagues. In the seven years since Bryce Harper debuted at 19 after one full Minor League season, teams have figured out that their best prospects can handle almost anything thrown at them.
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In the case of some -- for instance, Harper and Lindor and Correa -- prospects arrive and do more than simply produce respectable numbers. They're thrown into the middle of the lineup for contending teams and expected to be difference-makers.
We see it routinely. Last summer, it was Ronald Acuna Jr. helping the Braves make the playoffs for the first time since 2013. Rookie right-hander Walker Buehler made 23 starts for the Dodgers, who won the NL West for a sixth straight time. In 2016 and 2017, the Dodgers also got significant contributions from rookies: infielder/outfielder Cody Bellinger in 2017 and shortstop Corey Seager in 2016.
Do the Yankees make the playoffs in 2017 without Aaron Judge's 52 home runs? How important was rookie catcher Willson Contreras to the Cubs winning the World Series in 2016?
MLB Pipeline does a great job laying out baseball's top prospects and each club's top 30. But that's not the same as figuring out rookies likely to have an impact on getting their teams to the 2019 postseason.
Here are seven to keep an eye on:
1. Victor Robles, Nationals OF
This 21-year-old had an .849 OPS in five Minor League seasons and is an electric talent who steals bases, runs down everything in center field and teams with 20-year-old Juan Soto to give the Nationals two of the brightest young stars in the game. Even re-signing Harper seems unlikely to keep Robles out of the Opening Day lineup.

2. Forrest Whitley, Astros RHP
He hasn't thrown a pitch at Triple-A and might not, as the Astros have seen enough. He averaged 12.5 strikeouts per nine innings in the Arizona Fall League and 11.6 in eight starts at Double-A after serving a 50-game drug suspension. He has four quality pitches, including a fastball that touches 97 mph.

3. Jesus Luzardo, A's LHP
His calling card is the pinpoint control he has for a fastball that registers 97 mph at times and nicely sets up a terrific changeup. The A's are unsure how their rotation will line up behind veteran Mike Fiers, but Luzardo will be given every chance to grab a spot in Spring Training.

4. Alex Verdugo, Dodgers OF
No list of this sort is complete without a Dodger. President of baseball operations Andrew Friedman has overseen a system that has sent a steady stream of talent to the Majors, and now it's Verdugo's turn. He had an .863 OPS in 91 games at Triple-A in 2018 and held his own in 37 games in the big leagues (.706 OPS, six doubles). The Dodgers are so loaded he could start the season in the Minors, but he almost certainly will play a prominent role at some point in 2019.

5. Peter Alonso, Mets 1B
Mets fans have a long list of reasons to be excited, and this 24-year-old first baseman coming off a season of video game-like numbers is among them. Alonso hit 36 home runs in 132 Minor League games in 2018 and six more in the Arizona Fall League. He has produced impressive offensive numbers at every level in three Minor League seasons and seems likely to do the same thing at Citi Field.

6. Alex Reyes, Cardinals RHP
The Cardinals say they haven't decided whether he'll spend his first full post-Tommy John surgery season in the rotation or at the back end of the bullpen. Regardless, they intend to closely monitor his workload, making him one of those guys who could have a huge impact in the second half of the season -- and the postseason.

7. Keston Hiura, Brewers 2B
General manager David Stearns says Hiura will not open the season in the Major Leagues despite a 2018 season that ended with a .934 OPS in the Arizona Fall League. Even if Stearns lands a veteran to fill the spot until Hiura arrives, he could make an impact in Milwaukee at some point in the 2019 season.