Age: Both of these gulls appear to be in their first plumage cycle. The overall plumage aspect of the larger bird in front, with lightly checkered wing coverts and lack of gray scapulars support this. What of the smaller bird in the back with gray coming in on the scapulars? This is a 3-year gull, and adult-like gray scapulars is not unexpected in the first cycle.
Identification: These two species happen to be the most expected, year-round, residents on the Great Lakes and much of eastern North America. The smaller individual is a hatch year Ring-billed Gull. The silvery-white greater coverts are helpful with this age group, as is its size and incoming gray scapulars (via preformative or prealternate molt). The larger individual in front with paling bill and nondescript upperparts is a hatch year Herring Gull. Although this age group of Herrings is highly variable, there is no other expected species that bares resemblance to this.
Knowing these two species is a requisite for anyone hoping to learn gull identification in North America. The size difference here is remarkable and should be used as a benchmark for gauging sizes of other taxa.