Depends on the height, age, gender and such.
I for one am 14, female, 5'5", and weigh 120 lbs, alot of which is muscle.
Some kids in my studio/class weigh less, some weigh more, it all kind of depends on alot of factors (muslce is one, some kids I know freak out when they gain some weight but alot of the weight that a dancer, any kind of dancer, gains is usually muslce and not fat. Trust me, I learnt the hard way).
But since I believe you are a ballroom dancer (I don't know if that's correct or not, I just seem to recall that you are) then I don't think you should worry about your weight at all.
Besides, even heftier dancers can still be really good. One kid in my ballet class is a little (well maybe more then a little) on the hefty side and she is an awesome dancer and wins festivals and goes to provincials and all that dandy stuff. So I don't think it really matters all that much.