The one on the left is a third winter bird, but has gone through its prealternate molt and has developed a number of breeding traits - white head and neck, yellow/orange eye ring and yellow bill. It is also developing white tips to the primaries and possibly a white tail. It gray coverts, however are still coming in while its scapular and mantle are gray. These are traits of a third winter Herring Gull.
The second bird is a typical first winter with a new set of scapulars and mantle. Sides very bleached and the black tipped bill is not unlikely at this age (but it could still be all black). What is unique in this bird is its primaries - not black or even dark brown but a color more readily associated with a Thayer's. Even so, all other features are typical for a first winter Herring Gull.
Herring_Gull_1340m by Grandpa577, on Flickr
