Complex sentence: At the outbreak of the Second World War Livesey and Jeans were among the first volunteers to entertain the troops, before he volunteered for flying duties in the R.A.F., but due to his age he was rejected.
Split into simpler sentences: At the outbreak of the Second World War Livesey and Jeans were among the first volunteers to entertain the troops. He then volunteered for flying duties in the R.A.F. but due to his age he was rejected.