1965.
The letters AA identify the year of manufacture of your Marlin 39A golden Mountie as 1965.
You can look that up here http://oldguns.net/sn_php/marlinlookup.php
What year was Marlin 39A Mountie S/n 19968 made
Your marlin golden 39A mountie with the serial number you provided was made by marlin between late 1960-august of 1961.
The letter U prefix to your serial number indicates that your Marlin model 39a golden mountie was made by marlin from 1960-aug.1961.
The answer is 4500
your marlin 39A was made in 1965.
I can say that your Marlin model 39a golden mountie was made from 1953-1972.With the serial number that you have provided,yours was made in the year 1971.
1967
YOUR 39A WAS MFG. IN 1963
1963. sales@countrygunsmith.net
The prefix letters AC indicates that your Marlin model 39a Mountie was made in the year 1967.