Problem Statement: Aggression seems to be an extensive and serious problem among adolescents and emerging adults, negatively affecting both the victims and the offenders. In adolescence and emerging adulthood, a lot of factors affect aggression. In this study, five factors were examined: gender, life periods, identity formation, low self-control and self-esteem. Purpose of the Study: The aim of the study is to examine the relations between identity dimensions, low self-control, self-esteem, gender and life period (adolescence and emerging adulthood) with aggression. Method: For this purpose, a structural equation model was developed and tested. In this model, the dependent variable was aggression and the independent variables were demographic variables (gender and life period), identity dimensions, self-esteem and low self-control. Participants consisted of 240 adolescents (high school students--132 female and 108 male) and 244 emerging adults (university students--128 female and 116 male) and their age was between 15-24 years old (mean age = 18.99, SD = 2.62). The Buss-Perry Aggression Questionnaire, The Dimensions of Identity Development Scale, The Rosenberg Self-Esteem Scale, and The Low Self-Control Scale were used to collect data. Findings: Results of the overall fit indexes of the structural equation model revealed that fit indexes are at acceptable levels. Results of this study showed that life period, exploration in depth, ruminative exploration, self-esteem and low self-control significantly predicted aggression. According to model analysis, the best predictor of aggression was low self-control; the weakest predictor of aggression was life period. Conclusion and Recommendations: The present study provides important results. The first result is that aggression level changes according to life period. The second is that low self-control, self-esteem and some identity dimensions are crucial factors for aggression in adolescence and emerging adulthood. The results of the study provide several important explanations for counselors and educators. In order to reduce aggression, counselors, educators and mental health practitioners should consider identity, self-esteem and self-control. When counselors and educators prepare school-based intervention programs, they should consider the important predictors of aggression.