I've heard this works on Marlin rimfires, and I believe it's the case for all Marlin rifles... Take the first two digits of the serial number and subtract them from 100.
Subtracting the 1st 2 digits from 100 only works on rifles made 1972-present. On older guns you need to look up the date codes.
The system does not work with all rifles either. Many of the limited runs made by Marlin since 1972 have SN's that don't fit the system of subtracting from 100.