If you can do it (time, service commitments, training...) and it's a burning desire, go for it.
However, I held for 18 months...it was without doubt the best time of my life to date. No responsibilities, all the adventurous training I could fit in (5 weeks skiing in a season, gliding, diving...).
What I'm saying is - would you want to commit to something the RAF, for all its apparent moves towards "in service learning", isn't going to sanction, when you might not have to hold for that long? And if you were to hold for ages you'd be throwing away opportunities that you wouldn't be offered again once you got to the front line. Unless you were to fly VC-10s or join the Royal Flight.