The year can be determined from the serial number. Look on rimfirecentral.com. They have a section with Marlin and a file with an explanation of manufacturing years.
I bought a 39M in March that was in very nice shape for $300, but why would you want to sell yours? I also have a 39A that I got new while I was in high school in 1963. It has so many rounds through it that I probably need a new barrel, but I wouldnt sell it.