The age limit will not go up for either Service, trust me. The RAF have only just raised it, and the RN have had it at that level for at least 30 years. There are already far too many applicants, so the idea of raising it and thus having to handle even more is a non-starter.
Now you know that the RN and RAF are out of the way I'd concentrate on getting into the AAC. If you do all the right stuff you could get your grading done before you join RMAS and be as close as possible to a place when you complete. The AAC, like the rest of the Army, like to get to know their chaps before they turn up on day one. Get known.