>>/1974/
I really don't think so. Bonbi would have slipped up by now, over and over again. The chance of her not constantly somehow giving it away in streams or stories is basically 0.

 >>/1978/
If Black knew that she is actually 17, why would he not have said so at this point?
We know that he basically hates Bonbi now, so why would he still keep it secret if he knew?
If she were older than she said, somebody would have leaked it.