RCW 9.68A.090
Communication with minor for immoral purposes — Penalties.
http://apps.leg.wa.gov/rcw/default.aspx?cite=9.68A.090
(1) Except as provided in subsection (2) of this section, a person who communicates with a minor for immoral purposes, or a person who communicates with someone the person believes to be a minor for immoral purposes, is guilty of a gross misdemeanor.
(2) A person who communicates with a minor for immoral purposes is guilty of a class C felony punishable according to chapter 9A.20 RCW if the person has previously been convicted under this section or of a felony sexual offense under chapter 9.68A, 9A.44, or 9A.64 RCW or of any other felony sexual offense in this or any other state or if the person communicates with a minor or with someone the person believes to be a minor for immoral purposes through the sending of an electronic communication.
--And--
RCW 9.68A.011
Definitions.
(5) "Minor" means any person under eighteen years of age.
The code under which you have been charged and the definition of "minor" within that code don't appear to consider the separate code(s) regarding the age of sexual consent.
I'd say you're on the hook for the gross misdemeanor, but not the felony (assuming a lack of necessary qualifications).