Allow members of the armed forces under 21 to legally consume alcohol. I can serve the country but a bar can't serve me?

I joined the army at age 19 and am currently serving in the active duty army. I have signed on the dotted line to enlist in the military and have surrender many of my own personal freedoms for the betterment and protection of the United States of America and her people. I volunteered fully understanding that the call may require me to surrender my life in pursuit of that mission; however, I fully believe and am convinced that I have earned my place as an adult in this country. Currently it isn't legal for me to enjoy a beer with my colleagues. Somehow in the midst of all the training and sacrifice, I remain a "minor" in the eyes of the government. This is a bit perplexing, so I'm asking that all those who read this, do everything in their power to further this petition and make a change.