154 pounds (70 kgs) an average weight for 5"9?

Because you are asking this in dance, when it comes to lifts, you are a bit big. It isn't that you are too heavy for your height, you are just tall and your weight will make it difficult for you to partner. Your weight is average, but for a ballet dancer as your name implies, you are really too tall to be a professional. Most companies have a height restriction of 5' 7". I am not saying that their aren't dancer's 5' 8" and even a couple your height. The dancers that are your height have to be amazing because they would be too tall for corps de ballet and would stick out. They would also have to weigh about 125 tops.