It all depends.
There is no weight that a gymnast should weigh because every person is different. Some people have "heavy" bones, and some have "hollow" bones. It all depends on how much muscle you have, how tall you are, how "heavy" your bones are, everything. Chances are that if you are a gymnast, you aren't going to be fat because you are working out so much. I never worry about my weight. That doesn't mean that all i eat is like cookies or icecream, but as long as you eat fairly healthy, you shouldn't have a problem.
First off, everyone is different. I know people my height that weigh 20-30 lbs less, and are healthy, but if I am even 5lb less than I am (still a healthy weight, and done by lifting and eating healthy), I look gaunt. Its not pretty. So everyone is different.
Secondly, these threads are harmful and destructive to anyone with or borderline eating disorder. I cringe every time I see them. It becomes a "I weigh this much...oh, I weigh this much..." and a contest on who weighs less. It scares me. I've seen the damage an ed can cause and I'd hate to see anything on these wonderful boards that encourages it.
Thirdly...weight doesn't matter. Do you feel good? Is what you eat healthy and balanced? Does it include appropriate amounts of protein, carbohydrates, fruits, veggies, calcium, and good fats? Do you get regular exercise (this is likely, as you are in gymnastics)? These are the important things, not your weight.
WEIGHT IS NOT AN ACCURATE INDICATOR OF HEALTH OR FITNESS, especially for a gymnast.
The important thing is to make sure your body is getting the fuel it needs for such a demanding activity as gymnastics. I would be concerned if one of my gymnasts was under-fueling herself than I would be if she was over-fueling herself.
Boy there has been alot of threads on "how much should I weigh" lately.
Ok girls weight is just a number on the scale. don't get hung up on the numbers. That goes for clothing size too. Its just a number someone sewed into a garment. Don't get hung up on a number.
eat healthy and go to practice and you'll be fine. Remember muscle weighs more than fat does too. keeping your body healthy with the food it needs to do the exercise you do is the most important thing along with feeling good about yourself no matter what your weight is.