From the Hotline: Washington Domestic Partner Requirements
Question: What are the domestic partner requirements in the state of Washington?
Answer: Washington domestic partnerships are in the midst of changing. Effective June 30, 2014, all active same sex domestic partnerships will be automatically converted to marriages unless one of the partners is 62 years or older.
After that date, only domestic partnerships where one partner is 62 years of age or older may register with the state. These partnerships can be same or opposite sex and the individuals must be 18 years of age or older and capable of consent to the partnership. Additional information and a Declaration of State Registered Domestic Partnership can be found on the Secretary of State website.