I arrive at this thread rather late. The illustrations are excellent, and the extracts from Regulations illuminating, but do please be careful to read Graham's captions: a fair number are quotes from TF, VF, Militia or SR regulations and therefore not applicable to regular forces.
There is, however, a fair bit of sentimental codswallop written, spoken, and thought about boys in the army.
'The past is a different country' we are told. Indeed, as recently as when Frank Richards DCM MM 2ndRWF left school, it was at age 12 years to go straight to work. My grandfather who fought in the Great War left school at 14. The army recruited boys at 14, with a view to training drummers, pipers, trumpeters, buglers and tailors. Many such went on to high rank, and quickly. Mobilization Regs 1914 specifically permitted COs to take drummers etc under age on Active Service. 'Drummer' was not an appointment for any ordinary soldier, and it carried extra responsibility and pay.
Regarding Isandhlwana, I once did an analysis of the ages of those listed as drummers among the dead. I had been hoping to find evidence of lots of boys on the list, but was surprised at the maturity where there was evidence of age. Unfortunately, my Zulu War material is in the attic, but I could dig out the evidence if anyone is interested.
Don't believe all you read about the aftermath of Isandhlwana either: I studied at the feet of FWD Jackson, the great expert on the primary sources, and he was dismissive of most of the lurid nonsense, especially the D Morris stuff.
But, as I said, great illustrations.