Age: There is no reason to suspect this isn't an adult. On the underwing, we'd be looking for black markings on the tail, hints of dark centers on the secondaries and darker wing linings -- none which are seen here.
Identification: This appears to be a "white-winged" species, lacking black on the underside of the outer wingtip. The ghostly gray remiges, darkerst on the outer 5-6 primaries suggest Glaucous-winged Gull or a Kumlien's type Iceland Gull. The proportions -- long and broad wing, long tail, barrel-chested body, thick neck, and above all, the stout, bulbous-tipped bill -- all support Glaucous-winged Gull. This Glaucous-winged Gull was photographed in the Olympic peninsula region, and is the expected white-winged large gull here.