Turning 18 entails receiving the rights and responsibilities of adulthood to vote, serve on juries, get married, sign contracts, join the military--which includes taking on the responsibilities of life and death--and be prosecuted as adults. Adults from the age of 18 should therefore also be trusted to make decisions about alcohol consumption.
When adolescents are not taught to drink in moderation, they end up binge drinking when they do consume alcohol. It is better to teach youth to learn how to drink responsibly and hold them accountable for their actions as we do with driving.
These are only a couple of the reasons that the drinking age should be lowered to 18.