Many studies have reported a relationship between early age of onset and risk for later alcohol dependence (Chou & Pickering, 1992; Grant & Dawson, 1997; Guttmannova et al., 2011), suicidal behavior (Cho, Hallfors, & Iritani, 2007; Swahn, Bossarte, & Sullivent, 2008), and other problems (Hingson, Heeren, Jamanka, & Howland, 2000). Although there is evidence that after drinking is initiated, risk for additional problems is fundamentally genetic (McGue et al., 2006; Pagan et al., 2006; Prescott & Kendler, 1999), one must nevertheless begin drinking before such risk becomes relevant. Genetically informative studies have also found that risk of earlier onset is largely environmentally determined (Kendler, Schmitt, Aggen, & Prescott, 2008; Pagan et al., 2006), which could include exposure to drinking peers and lack of parental and other adult supervision.
