I haven't checked note for note yet, but I think this is the tune called Poor Soldier in the John Clare tunes in George Deacon's John Clare and the Folk Tradition (in G there; I think the Village Music Project has a copy, but you can see it here: Poor Soldier) It's also related to the song The Deadly Wars, which in turn is derived from Burns' Whwn Wild War's Deadly Blast Was Blawn, for which Burns' suggested tune was The Mill, Mill O. A copy of this tune is on our own Jack Campin's site and you can see it at abcnotation here: The Mill, Mill-O, and you'll see it's almost the same as the Distressed Soldier pdf. With a bit of luck Jack will come along with the ms details for his source.

It maybe Jeannie Robertson's Deadly Wars was the tune it reminded me of, but I'm pretty sure I've also played it for dancing.

Anyway, the fact that Burns suggested the tune dates it back at least as far as late 18C. Jack can probably give you a better date (or if not maybe I can tomorrow - I'm tired and off to bed now!)

Mick