Is it bad to be extremely obese at my age? side effects later on?

Yes, so eat smaller: It is bad to be obese at any age. For teens, many children's hospitals have weight loss programs geared to that age group. The pediatricians, along with dieticians and counselors, aim to get obese teens on a good life-long track of not over eating (one must overeat in order to get obese, meaning one must eat more than she uses), of having better self-image, getting new life skills, etc...