Refreshing honesty! I was a little younger than you when I decided that I wanted to the join the Army (much to the astonishment of my parents, who expected me to do something flaky).
May I suggest that you return when you are 16 and actually old enough to join the Army? In the mean time, I suggest you join the ACF (Army Cadet Force) if there's a detachment near you. This will teach you many of the rudiments of Army life, as well as giving you a chance to meet soldiers from all sorts of Regiments and Corps and get an idea of what you would like to do if you DO join the Army.
Meanwhile, there's a board on this forum especially for ACF/CCF - they'll be able to give you more advice.
And finally, for future reference, never, never, never reveal your age on a public forum if you are under 16. Mereminx, whilst I understand why you asked, it would have been more appropriate to simple assume that ARMY_MAD was a youngster. ARRSE is not immune from the Internet's dark side.