"...Usually have to be 'ex' military..." Nope. Nor is there any height requirements in the CF or at civilian clubs. I was running club ranges long before I got my CF RSO's ticket when Army Cadets still shot FN's, Lee-Enfields and .22's. Wasn't required to do any course either. CF or otherwise. That was a matter of having a great deal of experience before being Commissioned.
Anybody can be an RO. Learn the course(s) of fire, range commands, timings, etc and volunteer to run ranges at your club. Being able to speak clearly and loud enough to be heard through ear defenders over exhaust fans matters too.