The findings suggest an increasing difference between SEA and chronological age across the teen years as youth experience the normative changes associated with adolescence. Dating, sexual experiences, and substance use may be important factors in adolescents' SEA. The study found a positive linear relationship between SEA and chronological age; i.e., individuals who were chronologically older felt subjectively older than their actual age. Possible sources of individual differences in SEA among individuals of the same chronological age were identified. Adolescents who were dating an older partner felt older compared to other dating adolescents of the same chronological age. Sexually experienced adolescents felt older than their sexually inexperienced peers. An older SEA was also related to smoking in boys, higher alcohol use, and higher drug use. A total of 664 adolescents (322 boys) participated in the study. Chronological age was calculated as the difference between the date of birth and the date of the interview and ranged from 12 to 19 years. Data were collected in a medium-sized Canadian city in the spring of 2003. In a survey administered by trained and supervised interviewers who met with each adolescent, SEA was assessed with one interview item: "Compared to most boys/girls my age, most of the time I feel____." The age selected for the blank space was the SEA. Dating experiences, sexual experiences, and substance use were measured with other interview items. 2 tables and 31 references