The answer to your question - can a man be forced to determine parentage after the child reaches the age of 18 -- YES. Either parent or the child may bring an action. The statute uses the word "child," but then later defines child as "an individual of any age whose parentage may be determined under this chapter." Also, the chapter (RCW 26.26) later states that a "proceeding to adjudicate the parentage of a child having no ...second parent ... may be commenced at any time during the life of the child even after the child becomes an adult..."
What you can do is start a parentage action pursuant to RCW 26.26 (http://apps.leg.wa.gov/RCW/default.aspx?cite=26.26). DNA testing can establish parentage. The law does require child support.
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You can avoid this issue by filing the parentage action before the child turns 18. It’s always best to consult with a good family law attorney to discuss the details before you act. See my AVVO Legal Guides on parentage cases for more information about the legal issues raised by your inquiry. Click on my photo. On my AVVO home page click on "View Contributions" or scroll down further and click on "Legal Guides." Scroll down the list of my 29 Legal Guides and select the topics relevant to your question. If you like my answer and Legal Guides, please make sure you mark them as “helpful.”
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