We examine interactive effects of childhood sexual abuse (CSA) on heritable variation in age at first consensual sexual intercourse in a young cohort of 3,350 female and 2,724 male Australian twins. Consistent with hypotheses, genetic influences explained little if any variation in age at first consensual sexual intercourse for female twins reporting CSA (CSA(+)), with shared environment explaining 73%. For female twins reporting no history of CSA (CSA(-)), 39% of variation in age at first consensual sexual intercourse was explained by genetic effects, with shared environment accounting for 30%. For male twins, significant interactive effects of CSA on genetic and environmental variation in age at first consensual sexual intercourse were not observed. Overall genetic influences explained 51% of variation in age at first consensual sexual intercourse for male twins, with shared environment accounting for 8%. For both female and male twins, results from models that included conduct disorder as a covariate were near identical to results from models without conduct disorder.