QuestionIs it a good idea for children my age (age 12) to go on a diet? If it's not (or if it is) then what something I can do to lose weight. When is the best age for a young woman to go on a diet?
The best time to diet, if it is needed, is after you finish growing. Most diets being used do not just limit calories, they also limit the variety of foods that you eat. As you grow, your body needs calories to fuel that growth. It needs a lot of nutrients to put together a solid structure for your adult life.
People in the United States tend to eat too much rich foods. If you are concerned about your weight, switch to what I affectionately call a health-food nut's diet. Cut out the stuff made with sugar and white flour. "Have you found honey? Eat only as much as you need, Lest you be filled with it and vomit" (Proverbs 25:16). "It is not good to eat much honey; So to seek one's own glory is not glory" (Proverbs 25:27). Limit the amount of fried foods you eat. Eat lots of vegetables. In fact, make it a rule that you consume more vegetables than meat. So if you want a second helping of chicken, you have to eat seconds of the vegetables as well. Also make sure you eat a wide variety of foods. Don't get stuck in a rut.
What you will find is that the basic foods are more filling. You will have a harder time overeating, yet with a variety of foods, you will have plenty for a growing body. Only after you finished growing should you consider a calorie restrictive diet.