Age: Plumage and bare parts all seem typical of an adult four-year gull. The bright bill and all-white head suggest a bird in alternate plumage in breeding condition.
Identification: A black-backed species with yellow legs limits our choices to 3 species: Yellow-footed, Lesser Black-backed and Kelp Gull. There is very little contrast between the black wingtip and the black upperparts which hints at the darkest of black-backeds, Kelp Gull. The greenish-yellow legs (in contrast to the orange-yellow bill) also support Kelp over the other two species. The combination of broad wing with thick white trailing edge, decidedly small p10 mirror, clouded iris with apparent red orbital and strong bill all point to an adult Kelp Gull. Given the location, this makes perfect sense.