I doubt they'd cut you any slack; they need the same standard from everyone, remember. However, that doesn't mean you need to worry. Prepare as much as you can, relax into the interview and enjoy it. If you're successful, then great - on to the next step. If not, it's really valuable experience that you can use in another interview.
If you search on here, there're quite a few tips on interview success but fundamentally it's about you, your skills and your character - remember why you want to join the apprenticeship scheme and keep that as your motivation throughout. Good luck!
Enjoying it might be a bit of a stretch! But trying to relax would definitely be a good move. Although saying that I suppose "trying to relax” might be a contradiction in terms. Just turn up on time and hope for the best.
You'll likely be interviewed by 2 from the following:
MOD Band D or C2 Civil Servant
RFA Second Officer
RFA Senior Rate or Officer from your chosen branch.
They are experienced, qualified professionals and understand and allow for all manner of diversity, the kind of diversity that make some roll their eyes and that between the lives so far of 17 year olds and fossils.
I am not a recruiter, I just know shit.... sometimes Jack Shit.
Having the experience of going through SIFT twice now (2 different applications, long story), what I've gathered is that they don't expect you to have all the answers. Try and retain as much branch specific information, and answer as much as possible. Also ask questions too - show that you have a big interest in what you're going in for and that'll set you up well.
As ADXH said, enjoying it might be a stretch, but remember everyone is on the same side - you want to join, they want you to show yourself in the best light. It's okay to be nervous though.