I've been in for 19 years during which time I've trained recruits during basic training for 2 years and I've also trained recruits on trade training for 2 years. My advice would be to get as many qualifications as you can at school before joining and also get as fit as possible (running and upper body strength). A lot of recruits get discharged due to injury, there are many career choices the only areas of the army you can't join at the moment are the Infantry, Armoured Corps (Tanks) and Pioneers. What to go for is up to you! Check out the website which has loads of info. I joined at 16 as a Junior , you cannot go to Operational Enviroments until you are 18. My personal oppinion is that you should'nt go in until you are at least 18.
Good Luck and If you need any advice PM me
Karl