How young? My granddaughter is 14 and she weighs 210 at about 5' 9" tall. She has been heavy all her life. Always the tallest kid and always the fatest kid. She is comfortable with her size though.
The first thing we, as the adults in her life, did for her is have allergy tests done. It seems the more allergy foods she gets, the hungrier she is. Even now, when we see her trying to binge, we discover that she slipped on her allergy diet.
An example is that she cannot have chocolate because of the dairy and soy content. But she craves it. So we make sure she takes a Calcium/Magnesium supplement every morning to curb cravings and buy her treats. A dark chocolate that is dairy and soy free. She doesn't get a lot, but enough to know that it is not a forbidden food.
If you are smart enough to seek help, you should be able to monitor your own eating. Record all your food intake to discover your cravings. Ask your parents if you can see a doctor. Allergy testing could be an option, but not all doctors will go that route. Certainly a few other test will be done to discover a possible root to the problem. My son-in-law's sister was quite overweight which turned out to be thyroid related. She is now a slim, young adult, and you would never know that she had a weight issue.
Do see a doctor.
Do not skip meals, but set limits on portion sizes. Pick up a box of cereal and see what the portion size is. Most are about 3/4 cup.
Do discover the joys of moving your body. Walking, dancing (if it has to be in the privacy of your bedroom, so be it), sports.
Most of all, you need someone to encourage you and listen to you when things are bad. RL friends are best, but not always possible. Sometimes those skinny girls just don't understand, but some do.
July 3, 2014 - 1st day home after MI
Oct 4, 2014 Lowered my BMI by 3.6
1st Goal - remove an additional 3.2 from my BMI
2nd Goal - remove 5 more from my BMI
3rd Goal - remove 5 more from my BMI
Semi Final Goal - remove 5 more from my BMI