In the modern game, teams spot players at ever younger ages. They are put through development programs that are designed to squeeze every ounce of ability out of them. It is no wonder that some players burn out and fail to make the cut.
These young players are often highly exciting with huge amounts of natural ability. Every season, there are dozens of these young players making headlines as clubs pay truly gargantuan sums of money for teenagers with little top-level experience.
Many of them turn out to not have what it takes to survive at football's top table, but some do.
So, here is a list of the 10 best players under the age of 21 (that's under, not including) today.
So far, Romelu Lukaku's move to Chelsea has not gone so well. The striker has yet to score and has received little to no game time. So what makes him one of the 10 best players under the age of 21?
The fact that before he moved to Chelsea he netted 33 goals for Anderlecht certainly has something to do with it, especially considering he turned 18 less than two months before moving to London.
With Didier Drogba, Fernando Torres and Daniel Sturridge to contend with, Lukaku is too big a risk for Chelsea to bet on with Champions League qualification on the line. A loan move away could be on the cards per the Daily Mail, something that would do Lukaku the world of good.
He needs to be playing and scoring, and a move to a club like Hamburg would allow him to do so. Once he has some goals under his belt, Chelsea might be more willing to give the Belgian—who has 15 caps for his country already—a run of games.
If he starts playing on a weekly basis, Lukaku could find himself a lot farther up lists like this one.
Real Madrid centre-back Raphael Varane is just 18 years old, yet he is already proving to be a useful player at the Bernabeu.
Currently, Pepe and Ricardo Carvalho are in front of Varane in the centre-back pecking order, but Varane is taking every opportunity he gets. He has been impressive as a starter, both in La Liga and the Champions League and already has important experience from his time at Lens.
Most of his experience with Lens came before his 18th birthday, with some of it as a defensive midfielder with the club in a relegation battle; these factors appear to have sped up Varane's development.
The Frenchman could be hugely valuable in years to come. He already has an admirer in Rio Ferdinand, who tweeted praise (as reported by Goal.com). With Carvalho aged 33 and Pepe being something of a liability, the teenager could find an increased amount of game time next season.
The video is not massively informative; it's harder to find video packages for defenders, but it does give you some idea of how Varane plays.
Jack Wilshere has been out injured all season, but that does not prevent him from being one of the best footballers in the world under the age of 21.
Being English, there is a lot of hype around Wilshere and it is easy to see why. His range of passing is fantastic, his dribbling and close control are admirable, and he seems to have time on the ball, a quality not to be underestimated. He also doesn't seem to mind getting stuck in.
A year out of football has obviously not helped Wilshere's development. It may, however, have left him a little more composed and mature, something that will only improve his game.
Still only 20, Wilshere is young enough that he should be able to recover from his injury setbacks with relative ease.
Nineteen-year-old Brazilian Lucas has already attracted attention from Inter, with the club reportedly bidding about £21 million for the attacking midfielder, according to Italian newspaper La Gazzetta dello Sport (per Goal.com). He has also attracted interest from Bayern Munich and Manchester United according to Terra (per ESPN).
More than capable of scoring (check out his shooting) and creating goals, Lucas has already been a regular for Sao Paulo for two seasons.
While he might have a low profile when compared to some of his compatriots, Lucas could still prove to be a very big deal if and when he moves to Europe.
Twenty-year-old Swiss winger Xherdan Shaqiri secured a summer move to Bayern Munich, something the German giants must be pretty happy about.
With pace, skill and an eye for goal among his attributes, Shaqiri is in position to make a major impression on the Bundesliga and could be a player to watch at the Summer Olympics.
He has already shown he can perform against top sides. His two assists against Manchester United earlier this season helped FC Basel through to the next round of the Champions League and pushed the European giants into the Europa League.
It's pretty tough to get game time in Barcelona's phenomenally talented midfield, but Thiago Alcantara is not doing too badly for himself. He has started 14 La Liga games so far and appeared in seven more as a substitute, racking up three assists in the process.
He is only just beginning to make his way into the Spanish national side, but at just 20 years old, he has plenty of time to muscle his way into the starting lineup.
Barcelona is clearly quite keen to hold on to their youth team product—he has a buyout clause of €90 million.
Danish sensation Christian Eriksen is quickly proving to be a real find for Ajax. He first gained a global audience at the 2010 World Cup, where he was the youngest player in the tournament, and has been on the rise since then.
Naturally, he has been linked to just about everyone you would expect, including both Manchester clubs (per the Guardian). It seems likely that he will, at some point, make the move to one of Europe's top leagues.
For now, however, Ajax will be looking to get all they can out of a player who can bring a game to life with one dribble and provide fantastic passes.
Iker Muniain recently made headlines after putting in a fantastic performance against Manchester United in the Europa League.
Muniain is far from fully developed, but he is undoubtedly a player of huge potential. He has already forced his way into contention for the Spanish national team, no mean feat given the huge number of highly skilled midfielders in the Spanish arsenal.
Muniain works hard, constantly closing down and looking for mistakes to capitalize on; he can do so regularly thanks to great close control and good passing ability.
After making his debut at the age of 16, Muniain has grown to be an important cog in Athletic Bilbao's Champions League qualification push, something that has attracted attention from the likes of Manchester United.
Twenty-year-old Neymar is perhaps the hottest piece of real estate in football right now. The Brazilian is coveted by just about every major team in Europe and it is easy to see why.
The forward is quick, skillful and has a great eye for goal. He has found a great deal of success both for Santos in Brazil and for the national side, for whom he has scored eight times in 16 appearances.
Neymar has become a key part of the Brazilian side since the 2010 World Cup and could be a major player during the 2014 World Cup. Before that, however, it is likely that he will be strutting his stuff at one of Europe’s biggest clubs.
Mario Gotze is just 19 years old, but is already making waves in the Bundesliga. He played a key role in Borussia Dortmund’s league triumph in 2010-11 and got off to an impressive start this season with five goals and five assists in 14 games.
Unfortunately, Gotze is currently out injured and has been since the start of the year. The German attacking midfielder will be keen to make up for lost time when he returns, possibly next month.
Gotze has come into the German side since the 2010 World Cup and could be a key player come Euro 2012 this summer.