Science has shown that the earlier a person starts using drugs, the more likely he/she is to become addicted and suffer serious social and medical consequences. The reasons are complex. First, drugs affect the brain, and the brain is still maturing when a person is young—until early adulthood in fact. Thus, drugs can alter normal brain development. Second, people who use drugs when they are very young often have other problems that led to their drug use in the first place. For example, they may have difficult family situations or problems with depression or anxiety and use drugs to help them cope. Unfortunately, drug abuse just makes things worse in the long run and does not fix these problems. Third, using drugs can interfere with success in school, in sports, and in relationships with friends and family, creating more problems down the road.
Since early drug use can lead to later drug addiction and other problems, the best advice is not to even experiment with drugs. However, if someone is already using a drug, he/she should know that the earlier he/she stops, the more likely he/she is to avoid addiction and the other bad consequences associated with it. For more information, check out The Science of Addiction.