Is 188 pounds a good weight for a 5' 7 13-year-old?

No, 188 pounds is not a good weight for you. According to BMI (Body Mass Index) standards, you are either very close to overweight, or obese (depending on your gender). For males, those statistics are considered obese (91 out of 90 percentile, 90 being obese), and for a female, it is just below obese (85 out of 90 percentile, 90 being obese).