Adolescents’ sexual behaviors have attracted significant attention from developmental psychologists and researchers from related disciplines with the aim of understanding the factors associated with the behavior, its timing and outcomes. This study used a survey method to specifically estimate the prevalence of sexual activities, timing and the perception that adolescents in Dar es Salaam hold as to what would be the appropriate age to debut sexual activities. Data were collected using a pre-tested structured questionnaire from a sample of 389 adolescents who had a mean age of 17. ANOVA, Chi-square and regression analysis were used in the analysis. Results showed that 31.6% had debuted sexual activities by the age of 15.8. The appropriate age was reported to be 20.5. Demographic factors that were statistically associated with the dependent variables are presented. It is concluded that sexual activities are prevalent among adolescents in Dar es Salaam at early ages. This exposes them to the risk of acquiring sexually transmitted diseases such as HIV/AIDS because they are in no position to negotiate for safe sex. It is recommended that guidance and counselling on matters related to adolescents’ sexuality be highly reinforced in secondary schools by the responsible ministries and organs.