No matter the legal drinking age, teens will find a way to drink alcohol so having a legal drinking age only limits the public purchase of alcohol on teens.
Most teens do not start drinking until they reach high school so if the drinking age were lowered to 18, schools could offer more education about alcohol consumption and how to drink responsibly and parents could also try to guide their teens in the right direction by teaching them at home about responsible drinking before sending them off to college where they will be living on their own and most likely surrounded by parties and alcohol.
There is a division in college between the lower classmen and the upperclassmen by the fact that the upperclassmen are able to legally drink alcohol while the lower classmen are considered adults but cannot drink alcohol. The underage students are exposed to alcohol and they see their cohorts consuming alcohol and having a good time so they, too, want to join in, even if it’s illegal. It is more common for underage students to drink heavily compared to of age students. One reason for this is because underage students have limited access to alcohol so when they do have it, they consume as much as they possibly can. Of age students do not have to worry about access to alcohol so they can purchase and drink alcohol whenever they want so they tend to be more controlled.
Most politicians and their constituents do not want to lower the legal drinking age because they fear that it will lead to drunk driving which will then lead to more fatalities, but traffic fatalities are common to newly-legal drinkers no matter the age.
Many teens are hurt due to alcohol related injuries because they are afraid to reach out for help due to the fear of getting into trouble, but if the drinking age were lowered, teens would be less afraid to ask for help and the amount of teens hurt from alcohol related injuries would be reduced.
The economy would benefit from a lowered drinking age because then the age range of eligibility to buy alcohol would increase which would then increase sales because then more people could buy alcohol.