It's important not to confuse age of majority with marriageable age or with age of consent. These are three different concepts.
The original query was about the use of the term "minor" at a marriage in 1852. At that date, ecclesiastical law in England defined a minor as a person under 21, as any reliable UK genealogy website or textbook will tell you.
I can't comment specifically on usage over 100 years later in 1965, in the example you refer to. The age of majority was not lowered from 21 to 18 until the introduction of the Family Law Reform Act in 1969.