How fast will I lose weight?

I'm 12 years old, and I'm about 5 feet 2 inches (62 inches) . I weight 128.8 pounds and Im a little over wieght. When I pick out pants I go for size 5.. and t-shirts I get earthier medium or large. I want to be a size zero and not 5. Im doing this because I want to accomplish something and I want to feel confortable with my weight. Now, Im not looking fr someone to tell me I dont need to lose weight, but this is something I want to do. In my school everything is always about wieght and Im gonna prove I can set my mind to anything. I want to know If everyday I eat only breakfast, lunch, and dinner. (Healthy meals too) ... with no snacks... How fast will I be a size zero? Thnaks. xoxo, Lissa.