Partner age is associated with youth's sex risk behaviors and sexually transmitted infections. At present, however, it is not known whether the co-occurrence of other risk behaviors is associated with having older sex partners during adolescence and young adulthood. Using growth curve modeling, this study first describes the shape of the age difference between participants and their sex partners across adolescence and young adulthood in a sample of African American youth. Second, whether this model varied systematically by sex, mother's education, and high school dropout was tested. Third, whether age differences were associated with youth's self-acceptance, alcohol use, and employment trajectories over these two developmental periods was assessed. Finally, whether these associations had non-proportional effects over both periods was tested. This study modeled sex partners' age differences nonlinearly, with females being more likely to date older partners at baseline and over time. High school dropouts also reported older partners at baseline. Self-acceptance and the number of hours worked were associated with sex partners' age differences over time, with the effect decreasing over young adulthood years. Alcohol use frequency was also associated with having older partners over time. This study discusses the findings from a health perspective on youth's sexual development.