No they’re not too old. I watched 35mm prints of Monster Zero and War of the Gargantuas at the Alamo drafthouse Denver last summer and they were from the original US release in 1970. Both were showing various stages of fading to red, but both were still very watchable and for the most part had plenty of color left in them.

Also, I had my hands on 35mm prints of the 97 SE just a few years ago and they still looked brand new. Granted they had been professionally stored and refrigerated, but I can’t imagine even privately held copies would look much worse unless they had been seriously abused.