The simple answer was: "Old men make wars, young men have to fight them". When I joined (in late '40), the age limits for aircrew were 17½ - 23. Nearly all the prewar "short service" and General List people were killed early on: the RAF fought the war with boys born in the five years between 1919 and 1923.
After the huge contraction in 1946 - 49, it was left with: "a much smaller cake - but the same mix". It would be the mid to late '60s before all the "old wartime hairies" were phased out.
When I came back in '49, I shared a room with a nice young Cranwellian. He told me that the opinion of the Directing Staff there was: "We'll do no good with this Air Force till we get rid of all these old wartime people". Hope it wasn't true !