I'm not sure what arrangements there would be for invalidity pensions for the Boer Wars. I think there was some form of pension for WW1, but "invalidity" covers a multitude of things from war wounds to disease so I would think it was something of a lottery as to whether you were deemed eligible.
I've only looked at one page but the general impression is that poverty and ill health were showing up in their lack of fitness for combat.There were significant numbers on the same page who had TB. Others bought themselves out for £10 , a significant sum in those days, some were discharged as unfit, whilst there were a couple of desertions.
I did wonder if "indifferent" meant he was nothing special. FWIW he was born near Stirling in Scotland and in 1910 married my Grandfather's sister. He appears in the 1911 Census, but not in the 1921 although she described herself as married and the head of the household, so I must assume he was still alive in 1921. He would have been in his early 40s at the start of WW1 so probably didn't join up, so what happened to him is anybody's guess at this stage, although it's quite possible he simply legged it back to Scotland
Thanks again for the suggestions.