The present study investigated the association of age, gender, and family size with normative beliefs about aggression among South African adolescents from low-income areas. Adolescents (n = 229; mean age = 16 years; female = 61%) completed the Normative Beliefs about Aggression Scale. Step-wise regression analyses were conducted with age, gender, and family size as predictors of normative beliefs about aggression. Boys demonstrated greater endorsement of physical, non-physical, and relational aggression; as compared to girls. Living in an extended family was associated with less approval of aggression. Aggression reduction interventions with children from disadvantaged areas need to consider the role of gender and family-related factors.