Young motherhood is a risk factor for the child’s delinquency. Few studies, however, have attempted to unpack the mediating factors that underlie this relationship. The current study assessed factors that mediate the association between maternal age at childbirth (MAC) and the child’s delinquency using nationally representative data from the United States. Findings revealed that MAC predicted the child’s delinquency in adolescence. The link between MAC and delinquency was not mediated by parenting factors, neighborhood factors, or the child’s level of self-control. Instead, the MAC effect was completely mediated by the child’s level of exposure to drug-using peers.