According to the Rolleiclub site: http://www.rolleiclub.com/cameras/tl.../A-F_tlr.shtml there were Fs (Model: K7F4) being produced through the 70s and 80s. There are also various special edition 2.8Fs from the 80s and later, GXs beginning in the 80s.

If it was me I wouldn't worry about using a 60s one if it was in good condition. I have a 3.5E from the late 50s which I use regularly, and I can't fault the quality of the photographs (or the accuracy of the meter, for that matter).