All 3D-printed guns are young guns. The weapon as a distinct category didn't exist before May 2013, when Defense Distributed's single-shot Liberatorblasted them into existence. Before the Liberator, people printed parts and incorporated them into existing guns.
After the Liberator, designers expanded beyond its single-shot design. Now, a YouTube user with the handle Derwood is showing of a 3D printed semi-automatic weapon dubbed the Shuty-MP1.
Evolving from single-shot pistols to semi-automatics the first time took roughly 600 years, though with the existence of bullets and modern gun-making know how, it's not terribly surprising people were able to make the transition for printing guns in just two and a half years. That means Derwood's gun, made mostly of 3D-printed plastic parts, can fire an entire magazine of 9 mm bullets, ejecting spent bullet casings as it advances the next round into the chamber.