An "original" Rubik's cube would be more than 39 years old[...]
Actually, the first batch was produced in late 1977, so the oldest possible original Hungarian cube (Bűvös kocka) would be about 36½ years old.
[...]If your cube markings look like a clock face, then these are markings used by the manufacturer to identify the date they were made, which is quite a modern technique[...]
According to Arthur M. Merrill in his book "Plastics Technology, Volume 1", date code inserts
have been in use since the 1940s.