With so many prospects reaching the NBA while they're still teenagers, it's easy to forget that some of the league's biggest stars still have a lot of growth left in them—at least in theory.
Some of those stars won't get that much better, their development more or less plateauing after three or four years at the pro level. Others have only given us a hint of what they're capable of doing.
So which stars are destined for greatness, and which ones are as good as they're going to get?
We'll find out shortly.
But first, there are some rules to these rankings—there has to be some way of defining what counts as a young star, and the candidates can't be so good that their ceilings are already obvious.
So, the rankings won't include All-Stars (e.g. Derrick Rose), players 24 and over (sorry Ty Lawson fans) or any rookies (they already get enough attention).
With our pool of possibilities narrowed, here's a look at the 15 young stars with the most potential.
It didn't take 21-year-old Avery Bradley long to prove he was an exceptional perimeter defender and more than capable of hitting the corner three regularly.
In fact, Bradley impressed head coach Doc Rivers so much in 2011-12 (his second season), that he was inserted into the starting lineup to create a dangerous defensive one-two punch in the Boston Celtics' backcourt.
Though he doesn't have "superstar" written all over him, Bradley should become a reliable combo-guard who can start or serve as a sixth man.
You might think Nicolas Batum should be ranked more highly than Paul George when it comes to long athletic wings who can shoot.
He does have marginally better numbers, at least in terms of scoring.
But the doubts about Batum's upside have more to do with how much stronger he'll get and how that might affect his game.
If all goes incredibly well, you could be looking at a poor man's Kevin Durant. Otherwise, you're looking at a poor man's Danny Granger.
Thanks to the big-money deal he signed with the Portland Trail Blazers this summer, at least he won't be a poor man.
Some Minnesota Timberwolves fans will take issue with this ranking, and you can understand why.
Averaging 8.2 assists as a rookie is pretty impressive.
Ricky Rubio should become one of the game's very best playmakers, but there's no telling whether he'll ever become a great shooter or an elite defender (outside of raiding passing lanes).
For now, all we know is that he's already becoming one of the game's very best playmakers.
Making baskets is the open question.
You might not have heard much about Kawhi Leonard's rookie season given that he was one of many important role-players on the San Antonio Spurs' deep roster. But the fact that Gregg Popovich trusted him enough to start should tell you something.
The fact that he made almost 38 percent of his three-point attempts when perimeter shooting was expected to be his biggest weakness, should tell you even more.
If Leonard can improve his shot off the dribble, work on his mid-range game and become a stronger finisher, he has legitimate All-Star potential.
He's already an excellent rebounder and defender, so the blueprint for good things to come is there.
Derrick Favors isn't easy to evaluate because he hasn't played much more than 20 minutes a game in any of his three seasons, and his production has remained pretty steady in each one of them.
The 21-year-old has plenty of room for growth.
If he can add some range to his already explosive interior game, he could very well grow into one of the league's elite power forwards—at least in a best-case scenario.
But even in a worst-case scenario, Favors looks like he should be a borderline All-Star.
If this rank seems low for James Harden, it's only because we're measuring total upside rather than current talent levels.
Otherwise, he'd make the top-five easily.
Outside of an unfortunate performance in the NBA Finals, Harden has been consistent and highly effective coming off the Oklahoma City Thunder's bench—enough to win the 2012 Sixth Man of the Year award.
How much better Harden gets from here may depend to some degree on whether he remains in OKC or takes on a more prominent role elsewhere.
But after averaging 16.8 points and nearly four assists per game, we already have a pretty good idea of what this guy can do after three years.
He still has some room for improvement, but don't expect huge strides from here on out.
It's hard to find many players on this list who've already accomplished more than Greg Monroe.
The 22-year-old is coming off his second season in which he put up 15.4 points and 9.7 rebounds per contest, all while shooting the ball at a 52 percent clip.
These numbers are especially impressive given how much damage Monroe does from the post and mid-range areas.
This isn't a guy with Dwight Howard-like athleticism, so he's making the most of an impressive skill set.
That, however, also happens to be the only reason Monroe isn't higher on this list—as polished as his game already is, it's hard to imagine him improving significantly.
He could certainly replicate some of Zach Randolph's better seasons, especially as he transitions to power forward (to make room for Andre Drummond), but his life will also get a bit harder as defenders begin to take him more seriously.
Paul George initially made a name with his length and defense, but the 22-year-old's sophomore campaign proved he could shoot too—at a nearly 39 percent rate from three-point range no less.
With elite athleticism and the quickness to play at shooting guard, George looks poised to become a better version of Danny Granger.
That may pose some interesting questions for the Indiana Pacers down the road, but it has also spared George the responsibility of trying to carry this team early in his career.
He averaged 12.1 points and 5.6 rebounds in 2011-12, but there's nothing stopping George from becoming a versatile scorer capable of putting up 20 or more a night.
You could actually make the case that no one on this list has more upside than George, but it's just too hard to tell how much of it will be realized at this point, especially with Indiana's decentralized scoring approach.
Jrue Holiday's numbers won't jump out at you, but a lot of that has to do with the fact that he takes under 13 shots a game and plays for a coach (Doug Collins) who likes to see his team share the ball work as an ensemble unit.
But there's no questioning the 22-year-old's size, shooting ability and defensive contributions. He has already proven in three seasons to be a reliable centerpiece for the Philadelphia 76ers' offense, and he should only get better with Andrew Bynum drawing so much defensive attention on the low block.
Holiday isn't as quick as John Wall or explosive as Russell Westbrook, but he's a balanced player with a sophisticated skill set for his age.
The scary thing is that he's really yet to master some of the things that make point guards great, from shooting off the dribble to a steady drive-and-kick game.
Evan Turner may have been more prized at the draft (where he went to 76ers with the second-overall pick), but it has been Holiday—2009's 17th-overall pick—who's quickly become Philly's leader on the floor.
How soon we forget about Brandon Jennings, the guy who dropped 55 points in just his seventh game ever.
Three years later, it's just as unbelievable.
And though the Milwaukee Bucks' point guard hasn't turned into the greatest scorer of all time just quite yet, his production and efficiency took a nice jump in his third season, culminating in over 19 points per game, 5.5 assists and 1.6 steals.
His mid-range shot has become more consistent, and he has continued to improve his ability to finish around the rim.
The real test for Jennings will be to what extent he sheds that "shoot-first" instinct and evolves into a well-rounded floor general.
Even if his game doesn't go in that direction, though, the 23-year-old could still emerge as one of the league's very best point guards.
If we're really being technical about this, you could make a pretty good argument that Tyreke Evans should be first or second on this list.
When it comes to upside alone, there's really no telling how good this guy could be. He's an elite slasher with a quick first step and explosive leaping ability, but the real highlight here is that he does just about everything else you'd ask of an all-around star.
We learned as much after Evans' rookie season in which he added 5.8 assists and 5.3 rebounds to his 20.1 points per game.
His numbers have declined in the two seasons since, largely due to foot problems and an ever-changing role with the Sacramento Kings. When he returns to form and develops some range, watch out—Evans could become a household name in short order.
Eric Gordon is already in his fourth season, and he may not get that much better from here on out. But even if he has already reached his ceiling, it's still looking pretty high.
Gordon only played nine games in 2011-12 on account of injury, but he scored over 22 points per game the season before that, shooting over 36 percent from behind the arc in the process.
The good news about Gordon is that he's not just a shooter, though—he also has the strength and quickness to reach the basket and finish when he gets there.
It's easy to forget about Gordon after he was sidelined for so long, but he almost certainly remains the best young shooting guard in the league.
We always knew DeMarcus Cousins had the size and explosiveness to excel at the NBA level, but he has proven he can shoot too.
In fact, it's hard to remember too many 22-year-old big men who could knock down that mid-range shot from the high post with such regularity. Cousins could still extend his range even further, and that's what's so scary about his potential.
In just his second season, the 6'11" prodigy averaged 18.1 points, 11 rebounds and 1.2 blocks per game—numbers that would impress regardless of age.
If this guy's averaging a double-double already, it's scary to think about what he'll do as he enters his prime.
The Chris Paul comparisons proved to be pretty accurate after all.
Kyrie Irving's Rookie of the Year campaign was exceptional by any measure. His 18.5 points and 5.4 assists per game were impressive to be sure, but the efficiency with which he got there is even more remarkable. The 20-year-old made 40 percent of his three-point attempts, and he did all of his damage in just over 30 minutes a game.
As Irving grows more comfortable running the Cleveland Cavaliers' offense, we'll see his assist-to-turnover ratio improve, and he'll begin to look even more like Paul when it comes to distributing and controlling the flow of games.
If we were ranking how good these young stars are currently, about half the list would come ahead of John Wall.
But it's easy to forget he averaged eight assists per game last year, and it should say something that he has averaged over 16 points in each of his first two seasons without having anything on the order of a consistent three-point shot. He has gotten by thus far on account of his speed and athleticism alone.
Wall still has all the makings of an elite guard—good size at the point, great passing and a knack for slashing to the hoop.
Kyrie Irving got off to a quick start and is the better player for now, but Wall's upside is nearly limitless.