To be frank: I don’t believe a word of what OP is saying.
The reason is that there is no community where her situation would make any sense. She asks if she should wait until 21, implying that the norm would be to get married now at 17. But, she also has a boyfriend with whom she has decided they would want to get married.
So, is she chassidish with a boyfriend? Or is she MO but wants to marry at 17?