Age: The crisp, mottled brown, upperparts and body feathers, along with pointed dark primaries suggest a rather straight forward 1st cycle gull.
Identification: The frosted and checkered appearance of the upperwing coverts might call to mind Thayer's Gull, but this bird has already replaced a fair amount of it juvenile scapulars. You'd expect a Thayer's to do this late in the season when the upperparts are worn and primaries bleached. Also consider the paling bill and lack of pale edges to the primaries. Our March bird is a spiffy-looking Herring Gull photographed in mid-December. Chicago.
Here it is with another herring:
