I think the drinking age can be lowered slightly. Because in the United States you can drive at the age of 16. You can run for president at the age of 18. But drinking is 21 years old. Most people left their parents after attending college at the age of 18. So some of them will not restrain themselves. Many students secretly hide in the bedroom or drink at home, which will cause more problems.
Of course, if America lower drinking age. Crime statistics are likely to rise. So the answer to this question is two-sided, good side and bad side.