Hi
It would appear that some boys were acceptable at the age of 14 years.
Pte George Stirrat, Cameron Highlanders Band. The picture shows him when he was Drum Major of Queen Victoria School, Dunblane, when he commanded the QVS band at Olympia where he performed before the King and Queen in June 1914. His father Cpl Stirrat, Scots Greys was killed in the Boer War at the battle of Dronfield. George went to France with Cameron Highlanders as part of the BEF. He was in the field aged 14 and spent his 15 birthday on the battlefield. The Dundee Courier Jan 6 1915 headlines him as "Britains Youngest Soldier Wounded", and was in St Thomas' Hospital, London with shrapnel wounds to the leg.