What can i do to get a six pack at 16years old, fast?

The old-fashioned wy: You still need to do lots of core work to get the definition of the muscles, and cardio or dieting - to burn off/lose any overlying layers of fat. Being 16 years old - you have the advantage of youth, which allows most young people to lose weight and gain definition a little bit more 'easily' (though I am not saying it's easy) than say...A 43 year old ;-).