My oldest non-folding cameras date from 1936 and 1939 respectively - both Zeiss Ikon. Voigtlander introduced their Vito B in 1954 to replace the folding Vito II.

Certainly, the cameras being produced in 1960 were very different to those produced in 1950. But I don't think you can put an exact date on it. There were many small gradual changes to camera designs over the decade.