The earlier a person starts drinking the more likely they are to become alcohol dependent.

A fascinating study has investigated the relationship of alcohol dependence to the age of first drinking among 2691 twins living in Australia. In both males and females it was found that the earlier they started drinking, the more likely they were to become dependent on alcohol (41.1% of males who started before the age of 14 vs. 14.6% in those starting later, 25.3% for females starting early vs. 7.5% starting later). 

PositiveTip: Contrary to some advice given, avoid encourging young adolescents to try alcohol even if supervised.