Good advice from both posters - key being, there is no rush; which gives YOU time to seriously evaluate what type of flying YOU want to do.
I always find it helpful to look not just where you want to be now, but also in the medium and long term. What will be your employability should you leave; will you be able to continue flying as you progress in rank/seniority; will you become so specialised that you become limited in development opportunities...
That said, I have a number of ex-military colleagues who have reinvented their flying careers. C-130 captain who re-rolled to Chinook; C-130 Nav now flying commercially in Civ st; Nimrod pilot who went to civvy business jets, then less glamorous stuff; Chinook pilot who is now flying SAR in the gulf.
Don't dismiss one option over another simply based on supposition and stereotype. Really look into your choices (army, navy, RAF) and try to get some attachments/visits under your belt to ask the operators as many questions about their flying and service life.
At 17, the world really is at your feet. So don't feel too down.
Me, I went to OASC in 1995, graded 115, but thanks to the fall out from options for change, and over-recruitment, I was culled. I went on to spend 12 great years with the RAF doing other stuff and still found time to fly for fun.
