Lower the Drinking Age Back to 18

You can fight in wars, vote, pay taxes, get married, etc. at 18 years of age, but you cannot legally enjoy a beer until you are 21 years of age?
This is completely unfair, because everyone matures at different rates. The human brain does not automatically stop developing on one's 21st birthday. Most western countries have much lower drinking ages and they don't have alcohol problems.
If the drinking age were lowered to 18, then college students, military students, etc. would not have to act in secrecy when drinking. They would also not have to go to Canada to spend money, which could otherwise be spent here in America. This could save lots of money and increase business income by fewer police crackdowns and spring break destinations making more money from the college student population.