There is a James John who looks like he was pre-war Pembroke Yeomanry, then Horse Transport ASC before being commissioned into RAF. His medals were to be issued by the Air Ministry.
Granted temporary commission into the RAF 28th Sept 1918.
London Gazette Issue 31054; Page 14485.
Address is Sunny Bank Farm, Stepaside, Pembroke, S Wales.
Your man may be a bit young for that lot and it seems to be a popular name in Pembroke, but you never know.
Phil