The youngest boy to enlist in the British army was John Condon from Waterford, Ireland. He was 12 years old. In 1915 John Condon went with the Royal Irish Regiment to Flanders. He died during a German gas-attack near Ypres. His gravestone, nr. 6322 at the Poelkapelle British Cemetery in Belgium, mentions his age as 14, but that is incorrect. When he died, on 24th May 1915, he was still 13 years old. His birthday was in June.

Update: There’s a short article here with more info on his short life. Good to see the Peace School being renamed in his memory.