why do teens start drinking at an eary age? are there more under age drinkers than of age drinkers? what causes this problem

According to the National Institute on Alcohol Abuse and Alcoholism, the key reasons teens start drinking include: risk taking, sensitivity and tolerance, personality characteristics, hereditary factors, expectancies, environmental aspects. Check out this website for the details:

http://pubs.niaaa.nih.gov/publications/AA67/AA67.htm

This link to one of my previous posts explain how teens can beome alcoholics before the age of 21: 

http://www.breakingthecycles.com/blog/2009/05/28/how-teens-can-become-alcoholics-before-age-21/

This is another good resource website: 

http://www.surgeongeneral.gov/topics/underagedrinking/

Good luck with your report.