Panasonic didn't start importing bicycles to the USA until 1971,so it should be no earlier than that. At the other end, it should be no later than 1976, as those are the 1st generation Titlist and Thunderbird derailleurs, which got an update for 1977 (and I believe this model also shifted to 600/500 derailleurs by 1977). However, I'm leaning more to the middle of the range, based on the combination of down tube shift levers, butted hi-tensile tubing and the absence a chain guard on the chainwheel, as I thought thought the earlier version didn't use the butted tubeset and the later ones had stem shifters and chain guards. It looks like it may have aluminum rims, which would be an upgrade.