If the reason for his marrying so young was to secure land, which was often the reason for an unusually young age at marriage, there should be a marriage contract signed (with luck) by all four parents, and sometimes also by other family members as witnesses. (Articles of Marriage.) Unfortunately these can be seen only at the Manx Museum library, except for some included in the wills films.
Children aged over 14 but under 21 required the permission of parents or guardians to marry, but could have control of their own goods. As Frances said, the parent/guardian name is often not given in the parish register.

Sue