## 4 Discussion
### Analysis by Age Groups and Gender Differences
In this context, in the mixed U-10 category (under 10 years old), it is observed that those born in Q1 have nearly twice the likelihood of participation compared to those born in Q4 (OR = 1.856; 95% CI = 1.32-2.60). In the childhood stage (under 10 years old), various factors can condition children's participation in sports activities, including the influence of parental decisions. Some studies have noted that families with higher socioeconomic status tend to enroll children born in the later months of the year or those with delayed maturation less frequently [76], amplifying the inequalities associated with RAE [11]. The lack of autonomy at this stage means that sports participation does not only depend on the child's will but also on multiple external factors, such as the parents' knowledge of child development and their expectations regarding sports performance [11]. Some studies suggest that parents of relatively younger children are less likely to enroll them in sports initiation categories [77; 78]. In this early participation phase, there are no selection processes, and all children can join the activity, suggesting that parents' perceptions of their children compared to others might condition the manifestation of RAE [11]. In contrast, during adolescence, the selection process for athletes depends on coaches, who play a key role in identifying and developing athletic talent [1; 79]. When analyzing the male categories (Table 7 and Figure 5), there is an overrepresentation of athletes born in Q1 compared to those born in Q4, as indicated by OR values greater than one. This pattern is also observed in the M-16 category; however, although the OR is 1.139, these differences are not statistically significant, as the confidence interval (95% CI = 0.95-1.37) includes the value of one. This trend could be related to apparent differences in dropout rates in the M-14 category, as the dropout rate for athletes born in Q1 is around 10%, while for those born in Q4, it is only about 1%. This low dropout rate for those born in Q4 in the M-14 category could be explained by the fact that these athletes, initially perceived as disadvantaged due to their relative age, benefit from training and competing with relatively older peers [48]. This allows them to develop technical and psychological attributes, such as resilience, constant effort, and greater adaptability, which compensate for their initial disadvantage in physical development or maturity, allowing them to catch up with or even surpass their older peers in later sporting stages [80]. Regarding the female categories (Table 7 and Figure 5), a small effect is observed (OR = 1.324; 95% CI = 1.04-1.69) in the F-12 category (11 and 12 years old), which disappears in the F-14 and F-16 categories (13 to 16 years old). However, the effect reappears between the ages of 17 and 20 (F-18 and F-20), with a larger magnitude than in F-12 (ORF-18 = 1.483, 95% CI = 1.14-1.93; ORF-20 = 1.549, 95% CI = 1.12-2.14), and subsequently disappears in the adult stage (F-E). The results obtained in F-12 could be explained by the maturation selection hypothesis, which suggests that older athletes are associated with anthropometric advantages, such as taller height, and physical advantages, such as greater muscular strength [8]. Although it is recognized that maturation processes can vary considerably between individuals, it is likely that athletes with greater relative age experience transformations associated with puberty (approximately 12-14 years in girls) earlier than their younger counterparts [1; 73; 81]. Regarding the RAE increase in the F-18 category, it has been observed that the dropout rate among athletes born in Q4 (-40%) is almost double that of those born in Q1 (-20%). This fact could be related to what is known as the \"maturation selection hypothesis\" [1; 14; 82].