Traditional masculinity includes norms that encourage many of the aggressive behaviors whereas traditional femininity emphasizes aggression very little. In addition, the lack of emotional regulation as well as a poor impulse control have been related to aggression and, in particular, with reactive and proactive aggression. The objective of this study is to examine the role of gender stereotypes (masculinity/femininity) in reactive and proactive aggression, through regulatory emotional self-efficacy and emotion regulation. A total of 390 adolescents participated in a longitudinal study in Valencia, Spain. Structural equations modeling (SEM) was employed to explore a two-wave longitudinal model. The results show that femininity relates to reactive aggression through regulatory emotional self-efficacy and emotion regulation. This way, both emotional self-efficacy and emotional regulation mediate the relation between femininity and reactive aggression. Furthermore, reactive and proactive aggression relate positively and directly to masculinity and negatively to femininity. Therefore, violence prevention programs with adolescents should incorporate information to break down gender stereotypes and promote strategies to manage emotions. Such efforts may be helpful to reduce aggressive behaviors and violence.