I just found this that may be helpful. However I believe amy ancestor was not age 21 but they didnt have birth certificates!
"After 1753 no marriage of a person under the age of 21 was valid without the consent of parents or guardians. Clergymen who disobeyed the law were liable for 14 years transportation"

It follows that therefore they would be a minor under 21 yrs. Sorry if duplicated didnt have time to look through posts.