Samuel,
...and here I was thinking selection was all down to good looks and charm!
and it seemed to work. Most crews go on together even if the pairings were unlikely. On one crew the average age was about 44. The copilot was about 20.
That crew was never going to set the world on fire, on their own, but would have been a very steady and capable crew riding a nuc to war.
Others had an average age of about 25 with the old man of the crew usually the ex-kipper fleet AEO at 30.
Many crews were composed of direct entry commission aircrew who would depart at age 30 or 38 with very few destined for a permanent commission and full career in the RAF.