Complex sentence: At the start of World War I, although 43 and officially over-age, Munro refused a commission and joined 2nd King Edward's Horse as an ordinary trooper, later transferring to 22nd Battalion, the Royal Fusiliers, where he rose to the rank of lance sergeant.
Split into simpler sentences: At the start of the First World War Munro was 43 and officially over age, but he refused a commission and joined the 2nd King Edward's Horse as an ordinary trooper. He later transferred to the 22nd Battalion of the Royal Fusiliers, in which he rose to the rank of lance sergeant.