In this article, we contribute to the discussion on factors affecting adult participation in organized sport. To this end, we examine whether explanations regarding sport expertise can also add to the understanding of non-elite-level sport participation in young adulthood. Results from questionnaires (n = 572) revealed that date of birth and early sport debut positively correlated to strong sport performance during childhood, which, in turn, were correlated to strong sport performance and being selected for talent groups during adolescence. Finally, strong sport performance during adolescence was positively correlated to sports club membership as young adults. As relative age effects seem to remain throughout childhood and adolescence, we conclude that the underlying variable that affects the selection process and sport participation in young adulthood is date of birth. The results indicate that being active in sport as young adults is contingent on sport-specific variables previously not investigated in research on sport participation.