It was made in 1980
1957
If the number is T131774 then it was made in 1972.
If you are looking for the serial number and can't find one, then there most likely is not one. For a time Benjamin did not put serial numbers on their pistols. I also own a Benjamin that has no serial number and had to do some research to find this fact out. Reference: "Blue book of airguns"
It would really help if you stated the model number. Also most older Benjamin serial numbers began with a "B" or "H" or "T".
it was made in 1975
It was made in 1961
It was made in 1960
It was made in 1967
It was made in 1965
you need to state the model number not the serial number to get and estimate of value.
Serial numbers are usually on the left side of the barrel near the breech (loading port)