problem is that the 1807 marriage was a John mughtin (of ballaugh) to a Jane kneen of jurby - all the bapts (extracted) are for Thomas Moughtin + Jane kneen/neen
there was a John Mughtin illeg c/o Thos Moughtin(Ballaugh - affiliated 1806) + Elinr Kinread (who seemed to make a habit of it as noted as relapse)
There was another John Mughtin d/o John Mughtin + Elizth Mylea bapt Ballaugh 18050602 - no obv marriage but don't think marked as illeg in reg
I suspect the 1851 census was in error and a birth year of near 1805 is a better fit - catch is a miller needs an apprenticeship which costs money - thus probably not an illeg unles father was a miller