Background: The interconnection between chronological and biological age conspicuously affects adolescent athletic performance. Chronologically older athletes gain advantages such as bigger body size, while biologically older athletes excel in strength, speed, and power. The relative age effect (RAE) further exacerbates dissimilarities, fostering athletes born earlier in selection year. Competitive sports may enhance the likelihood of musculoskeletal pain, affecting performance, especially in older and early maturing athletes. Aim: This study aimed to assess whether RAE is present in a cohort of 13–14-year-old sports academy schoolgirls and boys. Furthermore, the aim was to investigate if pain frequency and maturity offset differed depending on which birth quartile the boys and girls were born in. Lastly, the aim was to study associations between chronological and biological age and sports performance in boys and girls. Methods: A total of 224/256 (135 boys, 60.3 % and 89 girls, 39.7 %) adolescent 7th grade athletes at a sports academy were included in this study. Participants were assessed based on anthropometric measures (height, weight, and BMI), sports performance tests (20-meter speed test, agility t-test, CMJ-AS, and handgrip strength test), and self-reported answers to pain questionnaires. Participants were divided into four birth quartiles (Q) to assess RAE, maturity level (early, average, late), and pain frequency using Pearson chi-square test. Chronological age, maturity offset, anthropometrics, and sports performance tests were all analyzed with Kruskal-Wallis test. Results: RAE existed among boys attending 7th grade at a sports academy, but not among girls, when compared to the age and sex-matched general population in Sweden. The analysis indicated no statistical significance between Q and frequency of pain, neither for boys (p=0.16) or girls (p= 0.11). Boys indicated no significant correlation between Q and maturity level (p = 0.07), while girls did (p =0.004). The boys’ maturity offset exhibited a high correlation with handgrip strength test (r =0.78), whereas girls had a moderate correlation (r = 0.46). Chronological age was found to have a low correlation with all four sports performance tests for both boys and girls. Conclusion: There was RAE among boys in 7th grade at a sports academy, but not among girls when compared to the general population. Height differences were significant, especially for boys in Q1 and Q4. Pain frequency did not differ between genders across quartiles. Both boys and girls showed significant differences in maturity offset across quartiles, particularly girls. Maturity offset was associated with handgrip strength, while chronological age had a low correlation with sports performance. The study underscores the need for further research on RAE in sports academies and musculoskeletal pain differences across quartiles, highlighting the importance of tailored interventions and training programs to support young athletes' development.