IAM,
It is going back a few years now but when I first applied to join the RAAF I was just finishing high school and had done not much with my life except finish high school. As I said before, I passed my pilot aptitude test but the psych was alarmed by my "...lack of life experience" and unsure how I would react in a military environment. So much for the military making a man of you, eh? I went back a year later and same story.
It was then that I joined the Army Reserve. I had a great time in the reserves and ended up as a Lieutenant. I went back to the RAAF and was able to demonstate my affinity for the military. This was about five years after I first applied, so you can see i was nothing if not determined.
So, you can see that being refused entry is not the end of the world and that you can work on aspects of your character that they may find insufficient.
It is good that they will let you resit the testing in the future. There should be no problems with finding out exactly where you went wrong and if they want to see you back then they believe that you can improve.
Best of luck with the future and keep trying. It really is worth it. Whatever category you end up in you will make some great mates, go to some interesting places and do things that your mates from school in their nine-to-fivers can only dream about or pay huge amounts of money to do.