Since age-groups in soccer often comprise children born within a two-year timeframe, characteristics that define the profile of a successful player may not be appropriate for the oldest or youngest players of the same age group. Therefore, this study aimed to determine to what extent performance was influenced by age, maturation and body size in elite soccer players with barely one year age gap. Anthropometry, 15-m sprint test, modified Barrow´s agility test, Yo-Yo intermittent recovery test level 1, countermovement jump, and handgrip test were conducted in players aged twelve and under (n=82, 11.1 ± 0.6 years; Mean ± SD) and between twelve and thirteen (n=79, 12.8 ± 0.6 years; Mean ± SD). A total score of performance, chronological age and age at peak height velocity were calculated. Descriptive statistics, Student’s t-tests, and multiple linear regressions were performed. The explained variance in composite score was greater in the older (54%) than in the younger (30%) players. Sum of skinfolds was the primary predictor of 15-m sprint and countermovement jump in the younger group whereas in the older group chronological age and body size appeared as predictors of performance (41%). Body size explained the variance in most tests in older players. In the younger group biological maturity status explained the variance in endurance (35%) and handgrip (59%) tests. In summary, chronological age and sum of skinfolds influenced most tests; however, predictors differed between age groups. These findings highlight the importance of assessing individual differences in young male soccer players regardless of their similarity in age.