Get a strong magnifier and read the hallmark, there'll be one somewhere on it but it might be too worn to read. By interpreting the symbols in the hallmark the date can be determined.....Google is your friend.
The alternative is to get the caseback off and note the serial number on the movement, but don`t mess with it if you don`t know what you're doing.
Judging from the style I`d say it's late 1960s, around 1967-70.
Paul