On further reading , the definition of "a minor" is under the age of 18 years. If the age of majority is at 21 the person is known to have reached "full age", and if under 21 but above 18, "under age", and under 18 years "a minor".
Maybe what could determine this, regarding this 1852 marriage certificate, would be in finding the baptism reistration of the person named and regarded as a "minor" on this certificate? One could then easily determine the actual age of the person at marriage.