The birds look like anywhere from 12-16 weeks of age. 12 and 16 week olds do not have a lot of difference in appearance, except that 16 week olds are a bit bigger. (I work at a poultry specialty store and we regularly have 50-200 birds of these varied ages there, so I've had a lot of time to see the differences.)
12 week olds cannot lay. The very earliest a hen can lay is 16 weeks. If a hen is laying, she's ready for a layer feed.
There is one difference besides size, the comb/wattle.