Previous studies have begged the question, Alcoholism: Clinical & Experimental Research has a study that attempts to provide an answer:
“The key finding of this study was that people who started drinking before age 15, and to a lesser extent those who started drinking at ages 15 to 17, were more likely to become alcohol dependent as adults than people who waited until 18 or older to start drinking,” said Dawson. “Past studies have often suggested that this association might result from common risk factors predisposing people to both early drinking and AUDs. Although the current study does not provide conclusive evidence that early drinking directly increases AUD risk, it suggests that it is premature to rule out the possibility of such a direct effect.”
“By controlling for a variety of confounding risk factors in their analysis, Dawson and colleagues were able to demonstrate that … early alcohol consumption itself, as a misguided choice or decision, is driving the relationship between early drinking and risk for development of later alcohol problems,” observed Moss.