The footballing world was a very different place in 2004.

Arsenal made history by becoming the first team to go an entire Premier League season unbeaten, while the world stood up and noticed Jose Mourinho after he led Porto to an unlikely Champions League triumph.

But that wasn't even the biggest upset of 2004 with that accolade going to Greece, who shocked the continent by defeating hosts Portugal to win the European Championships for the first time.

There was even a surprise in the Ballon d'Or as Andriy Shevchenko collected the coveted award over Barcelona duo Deco and Ronaldinho as well as 'Invincible' star Thierry Henry.

So, it would be fair to say that the beautiful game was pretty interesting in 2004 and a lot of the players we now recognise as icons started to come through the ranks that year.

Football in 2004

It was the first time that Cristiano Ronaldo and Wayne Rooney shared the pitch at Manchester United, for example, while Andres Iniesta and Carlos Tevez were also attracting hype.

And courtesy of Transfermarkt, we've been able to look back at the footballing landscape of 2004 in greater detail than ever, revealing the 15 wonder kids with the highest transfer value that year.

We've already looked at the most valuable players of all in 2004, but focusing on stars who were 21 or younger at the time shows there was so, so much talent coming through 16 years ago.

Carling Cup Final: Manchester United v Wigan Athletic

15 most valuable youngsters in 2004

Check out the 15 most valuable starlets down below and their eventual career-high value to see just how successful they were (spoiler alert: most of them absolutely smashed it):

15. Diego (19) - €10 million

Career-high value: €29 million

FC Porto v Chelsea

14. Vincent Kompany (18) - €10 million

Career-high value: €35 million

Christian Wilhelmsson (R) and Vincent Ko

13. Wesley Sneijder (20) - €10 million

Career-high value: €45 million

Ajax Amsterdam's Wesley Sneijder (L) pas

12. Emmanuel Adebayor (20) - €12 million

Career-high value: €25 million

Monaco's Uruguayan Ernesto Chevanton (R)

11. Rafael van der Vaart (21) - €12 million

Career-high value: €26 million

Rafael van der Vaart of AFC Ajax

10. Michael Essien (21) - €12 million

Career-high value: €38 million

Lyon's Ghanaian midfielder Micka?l Essie

9. Andres Iniesta (20) - €12 million

Career-high value: €70 million

FC Barcelona's Andres Iniesta (R) vies w

8. Daniele de Rossi (21) - €14 million

Career-high value: €38 million

AS Roma's Daniele De Rossi kisses his da

7. Carlos Tevez (20) - €15 million

Career-high value: €40 million

Argentine's national football team forwa

6. Cristiano Ronaldo (19) - €18 million

Career-high value: €120 million

Manchester United v Bolton Wanderers

5. Arjen Robben (20) - €20 million

Career-high value: €40 million

Chelsea v Norwich City

4. Robinho (20) - €22 million

Career-high value: €36.5 million

(FILES) Picture of Brazilian football st

3. Fernando Torres (20) - €25 million

Career-high value: €50 million

Atletico de Madrid's Fernando Torres cel

2. Jose Antonio Reyes (21) - €35 million

Career-high value: €35 million

Jose Antonio Reyes of Arsenal

1. Wayne Rooney (18) - €37 million

Career-high value: €65 million

Manchester United v Charlton Athletic

So many up-and-coming stars

What. A. Bunch. Of. Players.

Considering how many hyped youngsters that come and go in the modern game, it's astonishing to think that most of these starlets went on to justify all the praise before their 21st birthday.

Number one pick Rooney would go on to become United and England's all-time top scorer, while bronze medallist Torres won the World Cup and two European Championships with Spain.

Reyes and Robinho arguably never reached the levels of their fellow top 10 finishers, but to say their careers were still anything of a world-class standard would be to cruelly short-change them.

SV Hamburg v Real Madrid - Emirates Cup

Ronaldo: The pick of the bunch

But the most successful 2004 youngster can be found in sixth place... Ronaldo himself.

In an era where that name would immediately make fans think of the Brazil legend, Ronaldo launched himself to stardom at Old Trafford to flip the script by the time he was 25.

And frankly, if any of the current best youngsters in the sport can follow the career path of their 2004 predecessors, then we're in for an incredible next decade in the beautiful game.

UEFA Champions League Group D Fenerbache v Manchester United