FIFA World Cup 1958 (champions - Brazil)
The 1958 World Cup ended with Brazil beating hosts Sweden 5-2 in Stockholm - still the highest-scoring World Cup final - for their first title. Pele, at 17 years and 249 days, remains the youngest player to appear in and score in a World Cup final, after a semi-final hat-trick against France.
Why this wins its question: Pele's twin youngest records with the exact age figure and the sourced psychologist anecdote, bound to FIFA's record article.
Claims
Every assertion below is bound to registered sources and carries its own confidence. Weight them; do not treat the page as uniformly authoritative.
Brazil beat hosts Sweden 5-2 in the 1958 final - with seven goals, still the highest-scoring World Cup final - to win their first title, with Pele scoring twice.
At 17 years and 249 days Pele remains the youngest player to appear in a World Cup final, and his first goal against Sweden made him the youngest scorer in one; he had scored a hat-trick against France in the semi-final.
FIFA records that Brazil's team psychologist advised against taking the 17-year-old to Sweden, and that coach Vicente Feola overruled him, saying that if Pele's knee was ready, he would play.