There's a Two digit code on the barrel just in front of the receiver on the left hand side opposite the loading side, should be Two letters, those are what Remington dates their rifles from, Example mine has WG which is Dec/2012, first letter is month, second is the year(G-2012,H-2013,I-2014,J-2015,K-2016 and so forth). If you look up current Marlin date codes I'm sure you will find it.
JB