Before 1970, what was the minimum age at which one could see an X certificate film in the UK?

The original X certificate, replacing the H certificate, was issued between 1951 and 1982 by the British Board of Film Censors in the United Kingdom. It was introduced as a result of the Wheare Report on film censorship. From 1951 to 1970, it meant "Suitable for those aged 16 and over," and from 1970 to 1982 it was redefined as meaning "Suitable for those aged 18 and over". The X certificate was replaced in November 1982 by the 18 certificate.

Sometimes the rating of a film has changed significantly over time. For example, the French film Jules and Jim received an X rating in 1962 that was changed to a PG rating in 1991. In some early cases, films politically motivated received an X rating. The Battleship Potemkin was rejected for "inflammatory subtitles and Bolshevik propaganda" in 1926, rated X in 1954, and finally rated PG in 1987.