Birthdays and Caps: The Maturation Problem in Youth Development

Nigeria U-17 World Cup

On FIFA’s web-site promoting the start of the U-17 World Cup in Nigeria the event is hyped as a chance to “discover the stars of tomorrow.”  And while there is an impressive list of former participants (including, for example, Ronaldinho, Michael Essien, and Luis Figo) another look at the history of the U-17 World Cup offers more cautionary tales than burgeoning stars.

You might think that winning the Golden Ball or Golden Shoe at the U-17 World Cup would be a sure predictor of future stardom—and that is certainly the assumption of many professional scouts.  But since the first U-17 FIFA tournament in China in 1985 the winners of those awards include such decidedly non-stars as James Will of Scotland, Mohammed Al-Kathiri of Oman, Sergio Santamaría of Spain, Brazilians William and Adriano (not the Adriano of Inter Milan fame, but the journeyman whose career history includes nearly 20 different clubs—mostly in the lower levels of Brazil), and many others whose names should provoke amonst fans of world soccer that simplist of honorifics: Who?!?!

In fact, depending on how you feel about Landon Donovan’s failure to ever make it outside the US (he won the FIFA U-17 Golden Ball in 1999), the only clear success of the award winners from 12 editions of the U-17 World Cup is Cesc Fàbregas.  Now, some of the other winners have had degrees of success and there have certainly been many other good stories from the U-17 World Cup—but the general point should be familiar to anyone who pays any attention to youth development: the best players at 17 are rarely the best players at 25.  Which is what makes youth development anywhere such a puzzle.

And while there are many pieces to that puzzle, one of the most basic (but oft ignored) is the issue of maturation.  Age groups based on birthdays are really just artificial markers intended to group people at approximately levels in their physical maturation (something I’ve written about before in relation to claims of age cheats).  But physical maturation rates actually vary dramatically from one person to another—something that is particularly notable to those of us still scarred by showing up for U-17 try-outs weighing a buck ten (49.9 kgs) soaking wet and getting squashed like a bug by the tank who had been shaving twice a day since turning 10.  The tank and I were, according to our birthdays, the same age—but our bodies were years apart.


So what often happens at the U-17 World Cup, and in youth soccer everywhere, is that the best players are just the early maturers.  In many cases, they are as good as they will ever be at 17 while the late maturers still have years of physical development to go.  But one of the key (and, again, oft ignored) problem for any youth development scheme is that the early maturers often seem as though they will be the better players, and thus get a disproportionate amount of attention and resources (see, for example, Freddy Adu).  Malcolm Gladwell’s recent book Outliers, a tome ultimately designed to promote equal opportunity, begins with a clever example of this phenomenon known as relative age effects—something I though would be fun to consider in relation to US Soccer (since I’m an American and all…).

Relative Age Effects

In the ongoing discussion about how to best organize a youth development system, you rarely hear anyone talking about the importance of birthdays.  But for myself, having a day job as a developmental psychologist, the issue of birthdays and “relative age effects” seems right on point.  Relative age effects are a phenomenon where people gain some advantage because their birthday is on the early side of a cut-off defining a cohort such as grade in school or age-group for youth sports.  The idea is that as children those with early birthdays, although ostensibly the same age as others in their cohort, subtly benefit from being older and more mature than those with later birthdays.  The kid born January 1st is officially in the same age-group as the kid born December 31st, but in reality is a full year older.

This has some relevance to school, where children born on the early side of the year set to define a class will be (on average) more mature than children born towards the end of the year, and it has some relevance to sports including soccer.  In fact, there is an excellent summary of relative age effects and past versions of the U17 World Cup available at Science of Soccer Online, and lots of other good research out there on the phenomenon, but US Soccer also seems to offer a persuasive example.

Though the question is partially just a matter of interest for statistics nerds, it also has some very real implications for talent development and future national team success.  The issues at stake are engagingly described by Gladwell in Outliers, which describes the impact of relative age on sport success as having been first established among elite hockey players.  The basic finding is that a statistically significant disproportion of professional hockey players were born in the first few months of the year, presumably because they were more physically mature during age group play (which uses January 1st as a cut-off) and thus garnered extra success and exponential benefits.

Gladwell uses the example to illustrate a much broader argument about the ways success in society is not just a matter of hard work and individual merit—rather much of our success is due to fortuitous circumstances.  But elsewhere Gladwell also notes that as a Canadian he wishes the hockey powers-that-be would pay more attention to the relative age effect.  In essence, the current system deprives Canada of much potential hockey talent by arbitrarily privileging kids born in certain months.  This is not just a matter of equal opportunity, it is a matter of having really good national teams.  Think of all the Benny Feilhabers (DOB 1/19) and Lori Chalupnys (DOB 1/29) we might find if we paid as much attention to kids born in October, November, and December as we pay to kids born in January, February, and March.

Analyzing the US Rosters

So finding myself thoroughly bored a few months ago, I cut and pasted all the player pools on (as of 8/7/09) into a trusty excel spreadsheet and compared birth months.  The picture for the U15, U17, U18, and U20 teams is about what all the other research would predict:

age effects 1 2

The basic idea here is that US youth national teams are dominated by players born in the first quarter of the year.  Assuming that dates of birth are relatively randomly distributed and fundamentally irrelevant to true soccer potential, this basically means there is a systematic bias in our player development system (almost certainly unintentional and unconscious) towards older players.  The shame is that we are likely missing some great potential players who were born in December, and give up fighting the big kids before they ever fulfill their potential.

The picture for the older players is more complicated.  Including players from both the U23 / Olympic pools and full national team pools (I should note that I got a bit sloppy here because there is significant overlap in these pools, so some players were counted twice—though I don’t think that should dramatically change the distributions) the most popular time for women’s players to be born was July through September and the least popular was January through March:

age effects 2

I’m not sure what’s going on here.  It certainly could be that the women’s national team is more of a true meritocracy than other teams, though I kind of doubt that.  I wonder if it has to do more with the fact that during the years when most of the current national team players were growing up club soccer was a much more prominent place for female players to develop: the cut-off for club soccer were often August 1st to coordinate with school years.  But that’s just a guess.

Perhaps the most interesting thing I found in this birth date sifting is that if you want to play in a World Cup for the US you best not have the misfortune to be born in December.  For the U-17’s, for example, the roster of 40 players “in residency” (and thus presumably receiving most of the resources) includes zero with a December birthday.  Similarly, of the 93 players in the men’s and women’s US senior national team pools a grand total of one was born in December (if all things were equal you’d expect to have about 8 born in December—and in each of the 12 months).

The one US senior national pool player with a December birthday? Jay DeMerit.  For anyone that knows the Jay DeMerit story this fits perfectly with the concept of relative age effects: DeMerit never got a sniff for any US national team until he paid his own way from Green Bay to a London pub league and miraculously found his way to a starring role in Watford’s promotion to the Premier League.  Just think what he might have done if he had been born in January.

And if you pay any attention to the U-17 World Cup this month, which I recommend for the fun of it all, try to keep an open mind.  No matter how good a youth development scheme a country has, the nature of maturation and the artificial use of birthdays to define age groups means that as many “stars of tomorrow” are sitting home wondering if they’ll ever need to learn to shave as will be on the field in Nigeria.

Andrew Guest writes weekly for Pitch Invasion. He is an academic social scientist and soccer addict living in Portland, Oregon. Having worked (and played) in Malawi and Angola, he has a particular interest in Africa. He can be contacted at drewguest (at)

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