Age: All of these individuals appear to be adults. Given the amount of head streaking and the time of year, it is safe to assume they're in basic plumage (as opposed to "alternate" plumage).
Identification: We will ignore the farthest individual facing head on for the time being. This trio of yellow-legged species shows classic fieldmarks, and for the most part, identification is straightforward. Beginning with the palest individual -- the pale-eyed bird facing right -- we see a typical black ring around the bill tip and pale eye: Ring-billed Gull. Just in front of it is a dark-eyed bird with darker upperparts, slender bill tip with very light marks, and heavy smudging to the hindneck. The large p10 mirror (seen on the opposite wing just beyond the tail tip), and large boldly contrasting white tertial crescent make it a fairly standard Mew Gull. This species tends to show a proportionally larger eye on a smaller face. Farthest to the right, with straw-yellow legs is a larger birds with a dark eye, straight bill with signature black-to-red bill pattern near the tip. Everything about it suggests California Gull, with upperparts approximately the same as the Mew Gull. These 3 are our pale to medium gray yellow-legged white-headed gulls and should be learned well. Ring-billed and Mew are 3 cycle gulls, whereas California requires 4 cycles to acquire an adult-like plumage.
Now, if you guessed Ring-billed for the farthest individual, then you guessed correctly. The upperparts do appear a smidgen paler than the California Gull and if the two were standing at the same angle this would be more noticeable. The wider breast and slightly longer leg appearance also "feels" better for Ring-billed over Mew.