I'm guessing 1969. Marlin has used a few different date codes. With 1972 and newer guns you subtract the 1st 2 digits of the SN from 100 to get the date of Manufacture. A gun with 25****** would be a 1975 gun. For a few years prior to that the 1st 2 digits was the date. Prior to that it gets more complicated with letter codes.