The boys who looked least ready at 13 and 14 became the best bets. In one Spanish academy cohort, late maturers were far more likely to turn pro than early maturers, and every player who reached a top-five European league came from the late-maturing group.

The cohort, and how maturity was measured

The study followed every boy enrolled in the high-performance programme of one top-tier Spanish club during the 2010-11 season: 24 in the U16 squad, 23 in the U14 squad, mean age 13.53. Each had his biological maturity classified once, in February 2011, by a Tanner-Whitehouse II bone-age scan at Clínica Cemtro in Madrid. Boys whose skeletal age ran more than 0.51 years ahead of their birthday were tagged as early maturers. Those within ±0.50 years were on-time. Those more than 0.51 years behind were late.