There are important gaps in knowledge regarding factors contributing to the onset of child sexual abuse at different stages of the lifespan. The present study aimed to identify common and unique developmental, ecological and situational risk factors associated with the onset of sexual offending in adolescence and adulthood to determine what responses are required to effectively prevent its occurrence. The findings of this study reinforce that adolescents and adults, for the most part, are two distinct groups who may be motivated to sexually abuse for different reasons, and that their offending is influenced by different opportunity structures, constraints and experiences that characterise these life-stages. Findings reinforce the need for prevention efforts to be tailored across the lifespan. Emphasis should be placed on primary and secondary prevention efforts that are currently less developed in Australia, compared to tertiary responses.