Results suggest that adolescents who display rapid cognitive tempo, poor mental inhibitory control, and high impulsivity are more likely to be early-onset offenders. The findings confirm and extend previous research indicating that, among adolescents, offender and non-offender groups are reliably differentiated in respect to several measures of impulsivity. However, the study was unable to confirm that, within the offending population, there were significant differences between those showing early versus late onset, thereby raising intriguing questions for future research. A recommendation was made for a longitudinal research of youths identified as at-risk but not yet offending. Involvement in antisocial and delinquent behavior is common during adolescence, and for many years, researchers have suggested that delinquent behavior is a result of deficits in impulse control. The purpose of this study was to compare early-onset, late-onset, and non-offending youths on a range of measures pertaining to impulsivity. It was hypothesized that early-onset offenders would display poor mental inhibitory control; a more rapid cognitive tempo; perform significantly more inaccurately on a test of speed and accuracy; and be unable to withhold risk-taking on a gambling task. Participants in the study consisted of 129 Australian adolescents with each participant completing the Adapted Self-Repot Delinquency Scale, Stroop Colour and Word Test, Time Perception task, Accuracy Game, Risk-Taking Game, and the Eysenck Impulsiveness Questionnaire. Tables, references