Age: A large four-year gull with two generations of primaries showing. Primary replacement well underway. The 5 inner primaries are new, 2nd generation feathers, and thus this individual is in its 2nd molt cycle. All secondaries are 1st basic.
Identification: Overall the head, body and uppertail are very white for a four-year gull in early 2nd cycle. The thin tailband and overall peppered plumage aspect are reminiscent of Great Black-backed gull. The ginormous bill and stealth-bomber body with long thick legs all help identify this as a Great Black-backed Gull.
Indeed, the field-readable leg band "Black 3U4" trace this bird back to its natal colony of Appledore Island in Maine. More on this individual here.