senior cadets and a militia soldiers has always been a bit of a blank for me, but with a bit of hunting round the AWM website I think I now have a handle on it. The age group hasn't always helped - say in the instance of a lad in the vicinity of 18 years of age, who might be in the senior cadets or the militia going on his appearance. The cadets were grouped into junior cadets,12 to 14 years of age, senior cadets 14 to 18 years of age, and militia 18 to 26 years of age.
It appears, however, that the cadet uniform shirt did not have epaulettes (as in the example above), and the hat was often domed.
I still find the brass regimental number badge a conundrum. I'm not sure what the rule was with those badges so I will leave it for now and hope someone will comment on it.