The Ruger website, under customer service, historical data, pistols, will list the serial number ranges for each year of manufacture. Get the serial number, and hunt it down. Good luck.
Ruger has sn data on their web site.
Ruger's website has a sn function.
1964
If the Ruger website is working, it has sn data on it.
1965
It was manufactured in 1961.
Ruger will tell you if you phone customer service.
Ruger's website has extensive sn data. 75-175 or so
Blue Book of Gun Values
Primarily in the magazines; Mark II has a bolt hol open also
Ruger's web site has sn tables.
The Ruger website posts that information, under 'Product History'. See related link at the bottom.