Marijuana smoking often begins in the early teen years. This is particularly unfortunate as the young brain is particularly prone to damage.

Dr. Staci A. Gruber confirmed this at the 2010 annual session of the Society for Neuroscience in San Diego, California. She talked about a small but important study of 35 chronic marijuana smokers who averaged 22 years of age. 

Twenty of the subjects started smoking marijuana regularly before the age of 16. The rest delayed regular smoking until age 16 or later.