When I was discussing my application status with a recruiter last week, he explained to me that all applications are reviewed and given a score out of 5. Each trade has a certain score that your application must meet in order to continue on with your recruiting process. Armoured and Combat Engineer were a 3 and Infantry was a 4 (these numbers can vary as much as week to week). Since I only scored a 2 on my application - I applied for Engineer - he suggested that I should take some time and do some volunteering, team sports, physical fitness, as well upgrading education can make your application more competitive.
You have the time now to build your application to be very competitive.
I will have to agree with everybody else - finish high school.
Volunteer somewhere you would enjoy, and join a sports team and if you can get a part time job - keeping in mind that your school grades come first.
My :2c: