Objective: The purpose of this study was: (1) to assess the utility of age of first licit use and age of first illicit use as predictors of alcohol and drug use at ages 20 and 30; and (2) to examine the reliability of retrospectively recalled ages of onset of use.
Method: Subjects (N = 839) from the Rutgers Health and Human Development Project provided four waves of longitudinal data spanning the age range from 15 to 31.
Results: Retrospective recall of age of onset revealed a fair degree of relative agreement but a lack of absolute agreement because of an upward shift in recalled ages as individuals became older. Repeated measures ANOVAS revealed normative declines in alcohol and drug use from 20 to 30 even though individual differences in use remained quite stable across time. Regression analyses indicated that: (1) age of first licit use as recalled at age 18 did not predict alcohol or drug use at age 20; (2) age of first illicit use was a weak predictor of alcohol use at 20 but a fairly strong predictor of drug use at 20; and (3) neither age predicted use or use consequences at age 30.
Conclusions: In the general population, illicit drug use and heavier alcohol use are, regardless of age of onset, adolescence-limited phenomena for most individuals. Findings suggest that intervention efforts need to be aimed simultaneously at delaying the onset of illicit use and reducing use levels among young adult users.