The junior categories of sports generally represent a particular period of extreme complexity for children and young sports players, since this time coincides precisely with the phase of puberty. During this period, there are great changes to body size and composition, as well as changes to the functional capacity of children and adolescents. In addition, the literature points towards another complicating factor observed among young soccer players: relative age. The objectives of the present study were: a) to observe the distribution of dates of birth among junior soccer players over the course of the trimesters of the year; b) to compare the players' anthropometric characteristics and physical performance according to the trimester of birth; and c) to analyze the influence of the maturity offset in the process of selecting young players. Eighty-nine male soccer players from the under-14s category participated in this study. The physical tests applied were weight, height, maturity offset, 10 m sprint, 30 m sprint and Running-based Anaerobic Sprint Test (RAST). It should be noted that there was a great imbalance in the distribution of dates of birth, with an especially large presence of individuals born in the first half of the year (p < 0.001). Anthropometric, physical and maturational characteristics were compared according to the trimester of birth and statistically significant differences were observed only in comparing the maturity offset (p < 0.005). It can be concluded that the trimester of birth may not have a relationship with physical performance and anthropometric characteristics, even if there are differences in biological maturation.