Sorry, Brian, I was forgetting that we're into a new century - of course I meant 20th century. In actual fact, even prior to 20th century, there do not appear to be very many of these early marriages as most people had to wait until they could afford to marry. As for authority - the age of marriage was raised to 16 in the IOM by statute in 1933 - the Manx Act does not state what the age was previously but as the English Age of Marriage Act 1929 stated the age was being raised from 14 for boys and 12 for girls, and the IOM is usually just a few years behind England in such matters, I am fairly confident it was the same in the IOM. For an answer to most questions on tracing roots in the IOM, you can do no better than ourchase a copy of "The |Manx Family Tree" by Janet Narasimham, available from the IOM Family History Society.
Another point of interest is that prior to 1938, divorce could not be obtained through the civil courts but only by a special act of Tynwald and there are 12 or 13 divorces obtained in this manner between 1879 and 1937. However, even earlier than this, although divorce was rare, it was dealt with through the ecclesiastical courts - I have a copy (when I can lay my hands on it!)of a court report of an early divorce where the man was granted a divorce because of the wife's adultery - she was forbidden to remarry but the husband because he was the innocent party was free to remarry.