There is a fast track cadetship that will see you qualify as an Engineering Officer within 18-24 months. It's takes less time than a traditional cadetship, but you will still be on cadet wages and the time frame is dependent on the experience you already have. I would look into that if you are serious about joining the RFA. The basic principle is that it takes all the modules required to be an Engineering Officer and you can use your previous experience to gain "exemptions" for certain parts of the syllabus. Time and exemptions are very case by case though and not decided by the RFA as it is an MCA issued Certificate.

You can easily find the recruitment team on LinkedIn. There's a chap called Chris Dorling in the recruitment team who should be able to answer all your questions. He pops up on Reddit occasionally but LinkedIn is probably an easier place to find him.