Totally agree with TCF. QQ employ a staggeringly large number of ex-services aircrew and engineers (comissioned and non-commisioned) at Boscombe Down, and with your background and qualifications you would be in with a good chance I think. But perhaps consider going down the project management route as an alternative to technical work.
As for ETPS, not impossible at your age (it has been done apparently), but selection for the course is competitive and by all accounts it is incredibly hard work...