Funnily enough, I've found it the other way round.
An agency leaves out a critical requirement (age limit?).
You are encouraged to apply ( thereby qualifying as an agency sourced applicant! ) you spend a day filling in the airlines online application (several times 'cos it keeps crashing!) send it off, and wait excitedly for an indeterminate period of time.
Then the airline replies that theyre "velly solly bur you don have proper requiremen".
On the other hand I could just be a cynical old git!!