The United States Senate website contains information regarding the United States Constitution and links to the Archives for the Constitution, the Bill of Rights, and more.
Read this article created by the National Rifle Association of America (NRA) regarding the Second Amendment and your right to keep and bear arms.
The home page for the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF)
This page of the ATF website discusses the Federal legal minimum ages for buying firearms and ammo.