James O'Brien RWF Discharged 1908

Hello, Please can anybody help. I'm researching my wife's family but we are hitting a brick wall with her Grandfathers earlier life. His name was James O'Brien born in Dublin 07/07/1880 to John & Julia O'Brien. As far as we know he was discharged from the 23rd RWF 3rd battalion sometime in 1908. We think he was in Wrexham at the time because he married a Mary Ann Durkin from Wrexham on the 12/02/1907, Mary was 18yrs old and gave birth to their first child John (my wife's father) 2 months later.

James lied about his age and put on their marriage licence that he was 23yrs old and states his occupation as a Bricklayer journeyman (and not a soldier...!!) We have his details of his WW1 service but if it helps he was in the Royal Engineers a Sapper no 121684. any information will be much appreciated.

Dave.