In WA, open carry requires no permit. Possesion of a pistol by someone under 21, though, is restricted by RCW 9.41.240. You may want to hit the Washington board on this site. There are several WA-specific things, including police training bulletins reminding officers that OCing is legal. In Eastern WA, you should be more readily accepted than Seatte or Tacoma.
Should've mentioned, though, that you may not legally have a loaded pistol in a car without a concealed carry permit.
Man, I should really make sure I look up the laws before I type. I'd forgotten about RCW 9.41.240