What is the age of Winchester model 1912 20 gauge serial 15998?

Your winchester model 12 shotgun in 20ga was made in 1913.I should point out that the chamber of your 20ga shotgun is 2 1/2in.The winchester model 12 in 20ga was chambered in 2 1/2in until 1927.So caution is advised when shooting your shotgun!Do not attempt any modern day shotgun shells that have a length of 2 3/4in.