Starting in 1973, you could subtract the first two numbers of the serial number from 100 and determine the age or year of manufacture.
Before 1973, the first two digits of the serial number, indicated the year of manufacture. So, your model 25, like mine, was made in 1969.
Some online resources point to Brophy as the authority on dating a Marlin/Glenfield. But then Brophy states that the model 25 didn't start being produced until 1977.
i know this to inaccurate as my father purchased the Glenfield model 25 I currently own in 1969, the second year of production which actually stated in 1968.
Your serial number indicates that your Glenfield model 60 was made in the year 1974.
1975.
1975.
1971
1970
your glenfield was made in 1968.
With the serial number that you have provided,your Glenfield model 30A was made in the year 1977.
Your serial number indicates that your Glenfield model 20 bolt action was made in the year 1980.
1968
1980.
that would be a 1974 model
1967