While Ireland might be taking the oldest squad of any team to Euro 2016, there are plenty of young players to keep an eye on during the next four weeks.
For some hopefuls, they might see minimal game-time but others could be about to have the type of breakout campaign that Wayne Rooney had in the Euro 2004 group stages.
But who are the most promising players aged 21 and under to scout? We've had a look and while some of these players are already well-known to us and relatively established as seniors, there could be a gem or too.
Dele Alli
Little needs to be added about the England and Tottenham midfielder. After a breakout season for the PFA Young Player of the Year winner, the 20-year-old has goals and assists in his game.
His strong connection with Spurs and international team-mate Harry Kane could be crucial - especially if he is given licence to thrive in an attacking midfield zone. For the balance of the team, that might require a certain Mr Rooney to be cast aside which appears unlikely where manager Roy Hodgson is concerned.
Hector Bellerin
Another one we know well from his exploits at Arsenal, the attacking right-back profited from an injury to Real Madrid's Dani Carvajal to seal his place in the Spain squad.
With Spain's keep-ball stance, width from full-back is key and the 21-year-old is more than capable of providing that for Vicente Del Bosque's side.
Kingsley Coman
Just 19, the France winger already has multiple league titles from Serie A and Ligue 1 to the Bundesliga. Currently at Bayern Munich, where he is on a long-term loan from Juventus, the former Paris Saint-Germain youth graduate has gone from promising talent to one of the bright young things in world football.
His rise is that meteoric that he has already made it into a France squad for a major tournament already and scored his debut international goal in a friendly win over Russia in March:
He might not be an automatic starter for France this summer but could well grow into one if the opportunity arises.
Ante Coric
In 2015, the 19-year-old was named Croatian Hope of the Year, which is an award previously won by Luka Modric and Mateo Kovacic.
The attacking midfielder made it into Croatia's 23-man squad and while he might be a bit lower on the pecking order for a starting place, his potential is noted with rumours that ex-Croatia boss Slaven Bilic is willing to part with £10 million to bring his compatriot from Dinamo Zagreb to West Ham.
Jason Denayer
Injuries to Vincent Kompany and Nicolas Lombaerts means the defender, who is on Manchester City's books, is likely to see ample game-time for Belgium in France.
He's been on loan at Celtic and Galatasaray of late, but could do enough to impress Pep Guardiola this summer. He will be at right-back though for Belgium at the Euros as manager Marc Wilmots chooses to field Tottenham's Vertonghen-Alderweireld pairing centrally.
Victor Kovalenko
The Guardian's Ukraine contributor Artem Frankov describes the 20-year-old Shakhtar Donetsk midfielder "as the most talented and promising Ukrainian footballer of his generation – and probably the squad’s only real playmaker".
He has pedigree as he won the Golden Boot at last year's FIFA under-20 World Cup with five goals, including this hat-trick against USA:
Anthony Martial
It goes without saying that the 20-year-old France forward could make a real mark on home soil this summer after proving that his big-money move to Manchester United is proving to be cash well-spent.
He could play in a wider role or through the middle if required.
Leroy Sane
The athletic Germany forward, who is the son of a gymnast mother and footballer father, has been starring at Schalke which has propelled him into his national team's senior squad.
He already has three caps for the world champions at 20 and could be a surprise package from the bench.
Renato Sanches
The Portugal starlet doesn't need to be scouted because he's already turned down Manchester United in favour of a €35 million move to Bayern Munich.
The outgoing Benfica midfielder is already the youngest Portuguese player called up to a major tournament, breaking a record held by Cristiano Ronaldo for 12 years, and is seen as a future superstar if all goes well.
Raheem Sterling
Far from an unknown of course, it's easy to forget that the England and Manchester City winger is still just 21.
He's already amassed over 20 senior caps and appears to be a certain starter for much of England's time in France.
Julian Weigl
The midfielder has had a breakthrough year for an outstanding Borussia Dortmund side, earning praise for his passing range. He broke a Bundesliga possession record in May when he touched the ball 214 times in one match against FC Koln.
The 20-year-old has progressed to Euro 2016 squad membership for Germany and even if his game-time proves to be minimal, he is a successor to the fading Bastian Schweinsteiger.
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