Milo - the CWGC database entry for Felix Byrne says that his parents were from Plains, which is on the A89 Airdrie Road (thank you Google...) so that answers your now-disappeared question.
T18 - as Sgt Byrne was aircrew, the answer is no, that wasn't young. Although aircrew at the start of the war could be Leading Aircraftsmen (for instance), by 1944, all non commissioned aircrew would hold at least Sergeant's rank. I think I'm correct in saying that it is still entirely possible for a 20 year old to be a Sergeant if they're part of the non commissioned aircrew cadre.