I remember the book being set in Northern Ireland. The main character learns he’s apart of a world of magic of some sort. The magic is involved through speaking certain phrases. When the sorcerer use the magic, their bodies turns into iron. In the first book he turns 13 when he learns about this. He and some other people fight a guy who,s motif is being a clockmaker I think. I remember the main character saving the princess of the demons or something and by the second book they start becoming friends but the princess is manipulating him or something. She gives him the power to speak every magic invocation with the benefit of being so accurate in pronunciation in the words he barely turns into iron. I remember reading this as a younger kid but I moved away from the library so I can’t check what it was. Thanks so much.
Lost Classics of Teen Lit: Name That Book! 
It sounds like one of the books in “The Dark is Rising” series by Susan Cooper. The first book was Over Sea, Under Stone and the others in the other series were The Dark is Rising, Greenwitch, The Grey King and Silver on the Tree.
LikeLike