Hi,
Just an observation about his age . Many people lied about their ages, and if he looked a lot younger than he was I wouldn't totally rule out that he wasn't in the forces when he was in early 50's - my g grandfather was.
My G grandfather was transferred to the Royal flying corpse in 1917 when his true age was 51 yrs of age. He lied about his age on his forces papers back in 1914 . In 1914 he gives his birth as 1872 (making him look like 42 - when in fact he was 48 yrs old! He was born in 1866) He was discharged in 1918 (when he was 52)for being medically unfit.
Regarding the war, could your family have got the story mixed up over time and it wasn't WW1, but the second Boer war? (1899 to 1902)My other Great grandfather was in that one (and he was a coal miner, a Timberman in the pits to be more precise)
Kind Regards