As someone who legally sold a business as a minor (still a minor today), you are mistaken. Take a look at this article: http://en.wikipedia.org/wiki/Emancipation_of_minors
The law in WA (http://apps.leg.wa.gov/rcw/default.aspx?cite=13.64&full=...) reads "the petitioner [must indicate] that he or she has the ability to manage his or her financial affairs".