If it's a 20g hammerless it could be 1908. If it's a 10, 12 or 16 hammerless it could be about 1896, but some of the serial numbers are not in the remaining Hunter Arms records. OR (most likely) if a Field, Ideal, etc. it's about 1918.
Go to the Home Page and click on Shotguns, then Date of Manufacture. Also consider getting a Research Letter for more information.