I had a friend who was a member of an RAF Bomber Command crew and his fellow crew members called him "Dad" because he was 25 years of age with a wife and family.
He explained that he was more circumspect about taking on the risks involved because of his family commitments whereas his fellow crewmembers
Perhaps this was it, teenagers and a few years above feel immortal... and wouldn't have that fear that may arise with older folk.
I guess they had far more volunteers than spaces, and far less volunteers aged past the mid 20's, in those days marriage was usual by the early 20's? Many may have had young families.
Perhaps there was also an Aircrew cut-off age of course, but all of this combined conspired against those a little older.
the chance of surviving an ordinary tour of 30 missions unharmed was only 24%.
Again, can't find an accurate source for this information, but if I received this news with a young family, well, I'd damned well volunteer elsewhere.