In Washington, it is illegal for an adult (someone 18 or older) to have sex with a minor (someone younger than 16), even if the sex is consensual. The state also forbids certain sexual contact and intercourse between minors who are more than a certain number of years apart in age.

Can a 23 year old date a 17 year old in Washington?

As the other answers point out, it may technically be legal for a 23 year-old to have sex with a 17 year-old, because the age of consent in Washington is 16.

Can a 16-year-old date a 20 year old in WA?

In general, there are no laws that say when a young person can start dating another person (but there are laws about doing sexual activity with another person, which we explain below!) However, there are laws which make grooming children under the age of 16 a crime.