It's illegal, don't touch it. Age doesn't matter if it fires readily available ammo.
Determinants for Classification: Even though this weapon may exhibit a barrel shorter than 18 inches, it is subject to NFA regulations governing minimum dimensions because it employs a conventional ignition system and uses fixed ammunition that is readily available through ordinary channels of commercial trade. Consequently, this weapon would be classified as a “short-barreled Shotgun” and therefore all NFA regulations.
http://www.atf.gov/firearms/guides/i...e-firearm.html