Can a boy aged 19 Have s*x with a 17 year old girl Legally in Washington State?

Answer 1

Yes, you can.
The age of consent in Washington is 16.

It is illegal to engage in sexual acts with someone younger than 18 under three different sets of circumstances, enumerated in RCW 9A.44.096. Foster parents with their foster children; school teachers and school administration employees over their students; The third set of circumstances require all of the following situations occur in tandem: The older person is 60 months or more older than the 16- or 17-year-old, the person is in a significant relationship as defined, and such older person abuses the relationship to have sexual contact.