21 is the minimum age because a person’s brain does not stop developing until his or her early to mid-20s. Drinking alcohol while the brain is still developing can lead to long-lasting deficits in cognitive abilities, including learning and memory.
Alcohol use by those under 21 is also related to numerous health problems including injuries and death resulting from alcohol poisoning, car crashes, suicide, homicide, assaults, drowning and recreational mishaps. Not to mention that the early onset of drinking by youth significantly increases the risk of future health problems such as addiction.
Regardless of a person’s profession, underage drinking is still dangerous and unsafe. It is a fact based on biology not maturity or service to our country.
How alcohol affects brain: https://pubs.niaaa.nih.gov/publications/aa63/aa63.htm
Substance Abuse and Mental Health Services Administration. “Alcohol Dependence or Abuse and Age at First Use.” Washington, DC: Department of Health and Human Services, Office of Applied Studies, October 22, 2004. Read the full study here.