The ambiguity of late onset -- Life course criminology and offending trajectories -- Adolescent onset of problem behaviors -- Adult onset of problem behaviors -- Theoretical explanations of late onset -- Methodological issues in studying late onset -- Designing a study of late onset -- Identifying early, normative, and late onset: findings from the NYSFS -- Predictors of early, normative and late onset: patterns of initiation for substance use and offending -- Late onset: mountain or molehill?.