Pontious, not strictly true. Many wait unti they are older to go aircrew and do have plenty of technical experience, in many cases much more than a lot of the Engo's around who have nothing but a piece of paper from a University and couldn't tell one end of a spanner form the other.
Oddly enough we had a Corporal, with whom I was friends, who went that route and became an Engo.
In discussion when he left I said jokingly i'd still call him a W**k*r when he was promoted... roll on 3 years and walking into a hangar in RAFG and there was a new Flt Lt L*****, walking towards him from out of his line of sight I called out L***** you W**k*r!.. LOL, we had a good laugh and chat catching up on things... it was last time I saw him in my career.