Roughly the chances are about 2% from past applications to cadet places. Someone has to fly these aircraft so why should it not be you? From my experience taking into account their experience levels the FPP's are very capable. As one of the youngest potential FPP's I would say make yourself stand out by doing something other than study and aviation. I know it's hard having broad experience when your young but having a passion outside of flying is a real positive. Final bit of advice would be take it one step at a time and you will achieve your goal. Often it's not as you plan it but take a easy going approach and you'll do just fine