I noticed that on his Army Service Record that he joined in June 1912 aged 17 and 6 months

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He was posted to Buddon on 17th August, 1913. Now Buddon is in Scotland near Carnoustie and checking on Scotlands people there was a marriage of a William Moore Gibson (using the exact match) in 1915 however it doesn`t work with spouse named Flora. Her forname (or at least one of them) begins with B. Got it - Bridget!!
It may not be him but it is looking more than likely.
Mo
Added: I have just worked out that her surname was Peters.