The "S" prefix will date your 39 to the 1927-31 era.
You do not state what model of marlin you have?I can say that if you have a model 1881,1888,1891,1892,1893,1894,or 1897 marlin with the serial number you provided it was made in the year 1900.
I would try the marlin firearms web site for a answer to your question.PLese be sure which model marlin you have.
1960
A serial number would be required to identify the year of manufacture of your Marlin model 60.
There were approximately 250,000 model 94's manufactured between 1894 and 1935. With a serial number of 21 million, your's wasn't one of them.
1961
mod 97 ser 339974
i have a marlin 30-30 model 1893 ser# 2113xx can you tell me the value of it thanks rick
U is for 1961
$250 ish
With the serial number that you have supplied,your Marlin(Glenfield) rifle was made in the year 1980.
I jhave a marlin leveraction 25x20 1894 model in great condition can you give me a range of how much it is worth can send photos