At 20 years old, Atlanta's Ozzie Albies made it to the Major Leagues for 57 games in 2017, and for most of that time, he was the youngest player in the bigs. (Washington's Victor Robles, five months younger, later received a brief September call-up for 27 plate appearances.)
If you knew absolutely nothing else about Albies' season, that alone would be impressive, because it's extremely difficult to get to the Majors at 20 years old. At that age, Joey Votto was in Class A. So was Nolan Arenado, and Eric Hosmer. Plenty of other current stars were in college. Since 2000, just 0.3 percent of all non-pitcher plate appearances taken have been from players 20 or younger. It's rare.
Even if you do get to the Majors that young, it's easy to struggle. Gary Sheffield hit just .247/.303/.337 with five homers as a 20-year-old in 1989; Ivan Rodriguez hit only .260/.300/.360 with eight homers at 20 in 1992. Even the great Jose Cabrera hit "only" .268/.325/.468 in 2003, essentially league-average. It's really, really hard to produce at the highest level when you're that young.
But Albies didn't struggle. The second baseman succeeded in his 244 plate appearances, hitting .286/.354/.456 with six homers and good defense. Using a park-adjusted stat like Weighted Runs Created Plus (wRC+), where 100 is league-average for that year, Albies had a 112 wRC+, or "12 points above average."
At the risk of putting a ludicrously unfair amount of a pressure on a talented young player by comparing him to some of the best who have ever stepped on the field, that's not just impressive, it's historically notable. If you do what Albies just did, you are almost guaranteed to have an above-average career. (Almost, of course.)

We looked back at every player season since the birth of the "modern era" in 1920 to find seasons like Albies just had, which we define as being "age 20 or younger, with at least 240 plate appearances, and with a wRC+ of at least 110.
We found only 33 such seasons, by 30 players (four did it twice by age 20, which is its own separate kind of impressive)... and the names are absolutely stunning. We're talking about today's best stars, some of the most inner-circle Hall of Famers ever, and several others with impressive, All-Star careers. 

Twenty-eight players did it prior to 2017 (let's make sure to credit Boston's Rafael Devers and his own impressive 2017 here as well). They break down into the following categories.
Hall of Famers (14+1)
Fourteen of the players are already enshrined in Cooperstown, and some of these guys are more "legends" than they are "baseball players," all-time greats like Williams, Mantle, Griffey, Robinson, and Bench. Mel Ott his 511 homers in an era very unlike the power-happy game we see now. Mathews hit 512; Foxx had 534. These are literally the best of the best, and they made it clear at a young age.
We'll also include Alex Rodriguez in this group, because as a three-time Most Valuable Player and 14-time All-Star, his Cooperstown case will be considerable when he's eligible in a few years.
Active Stars (5)
It's obviously premature to discuss Bryce Harper (who did it twice!), Michael Trout, Carlos Correa, Giancarlo Stanton, and Jason Heyward in terms of eventual Hall of Fame induction, but Trout in particular isn't just the best player on Earth right now, he looks certain to be an inner-circle all-time great. We'll note Heyward's Chicago struggles and suggest that it's at least possible that four of these five could end up in Cooperstown one day.
Between them, these five have 13 All-Star appearances, four MVP awards, and three Rookie of the Year awards -- and the oldest one is Heyward, only entering his age-28 season.
Non Hall of Fame All-Stars (7)
Seven others didn't quite have historically great careers, though by making at least one All-Star game after age 20 it was clear they were still valuable. Pinson, for example, played for 18 years and received MVP votes in five different seasons. Cedeno was a four-time All-Star; Conigliaro could have been one of the all-time greats, though his career was tragically impacted when he was hit in the eye by a pitch at 22.
Other (2)
Being productive at 20 years old didn't work out for everyone, of course, because injuries are always a risk. Derrell Griffith hit well for the 1964 Dodgers, but never played again after 1966 due to a shoulder injury. Clint Hurdle, now the Pirates manager, was the No. 9 overall pick in the 1975 Draft, then also had a strong age-22 season (.294/.349/.458, 118 wRC+), but injuries and inconsistency prevented much after that.
Let's be clear: The point here is not to say that Albies is guaranteed to be the next Mantle or Mays. He might not even be the next Claudell Washington. There are so many ways this could all go wrong, because baseball never makes it that easy, and doing it for 244 plate appearances is not the same thing as Trout doing it for 639 plate appearances at age 20, or even Pinson doing it over 706 times up when he was 20.
But what you can say is that based on what he's shown so far, it's very easy to bet on him to go on to do big things. It's hard to get to the Majors at 20, after all, and harder to succeed while you're there. If you can do both, history shows that you've done something very, very special.