Just to clarify for OP's benefit:
The age of consent in Washington is 16. However, there are other factors involved. One of them says that if the child is between 16 and 18 AND their partner is at least 60 months older, sex between them is illegal. If one is 17 and the other is 23, then there is more than 60 months between them, so it's illegal.
In addition, there are other laws involved which are sometimes prosecuted. One of them involves communication with a minor for immoral purposes. This one involves communication with someone under 18 for 'immoral purposes', so assuming that they communicated in some way, THAT law could be applied, as well.