I was reseaching this problem recently and came upon this on the GRO site
"Age of Marriage Act 1929
An act to make void marriages between persons either of whom is under the age of 16. Prior to
this change in legislation girls could marry at 12 and boys at 14 but marriages at such early ages
were almost unknown. Sixteen remains the lower age-limit today, contained in the current
legislation, the Marriage (Scotland) Act 1977. Scots law still has no requirement for parental
consent. There is no upper age limit."
The link is: http://www.gro-scotland.gov.uk/files/history.pdf