I think you uploaded the pictures in the wrong order:
agree with you, second is an immature winter Herring Gull.
Caveat: with such an uniform grey mantle, pale iris and very limited pale streaking to the head (assuming it was taken in February), it looks more like a 4 cy to me, despite extensive dark in tail.
First picture (the flying gull) has a large bill suggesting a GBBG first, but:
-pale eye in an immature bird
-extensive dark tail (a GBBG would say its uniform coloured)
-just visible pale grey feathers om upperparts
-washed out, fine barring on greater coverts would be unusual for a GBBG, typical, they should show extensive white ones with distinct contrasting barring
makes this another Herring Gull for me. Bill can be described as monster for this species, but its within variation. Bill would be on the waek sidefor a GBBG (but also within variation, I think?)
Leave ageing (2 cy or 3 cy) of this immature Herring Gull to more experienced people
1. = 3cy HG (inner primaries and secondaries lacking large white tips)
2. = 4cy HG (tricky to age without an open wing but plain pattern on greater coverts and much white in tail and tertials suggest a 3rd winter).