Yes, it is legal. The age of consent in Washington State is 16. For your reference, RCW 9A.44.010 sets forth the definition of "sexual contact" and "consent."
As the previous answers have stated, the legal age of consent in Washington is 16. So, consentual sex between you is legal.
There are some exceptions, including if the person is over 16, but under 18 and the other party is their teacher, foster parent or is in some supervisory position.