If you can legally drive, die for your country, or vote for your president, I think you should be able to drink. It doesn't make any sense how they are responsible enough to drive a vehicle or fight in a war, but they're not responsible enough to drink a beer.
Lowering the drinking age to 18 would be such a mistake considering that 18 year olds are not mature enough to be drinking, especially since they will still be in high school. They dont need to have access to something that could distract them from school and not getting things done because they want to get drunk.
I think that the image of alcohol, and it's associated "coolness" would still remain intact despite it's legality. Making the age lower would only expose more immature teenagers to dangerous situations . It would be easier for people to consume alcohol without needing to find alternate ways of purchasing it.
I think that if the drinking age was lowered, it would be easier to obtain alcohol. This would let more people abuse the substance. However, some might argue that by lowering the age-limit it would therefore make alcohol less taboo and "cool". I think that alcohol has been around long enough to retain it's stigma, it's image, and lowering the age-limit would only broaden the amount of people drinking the dangerous and easily abused substance.