He is a cockerel. Though I disagree with some others, he is not older than 4 months. They all look 12-16 weeks old. He’s pretty bedraggled, does he get picked on? It’d be easier to clarify sex if his feathers were full, as you’d likely be able to see the start of pointed saddle feathers coming...
12-16 weeks (3-4 months) seems about right.
They are all pullets, except Emmerson, who is a cockerel.
Not sure on breeds or mixes, though they do seem mixed. Two definitely have Transylvanian Naked Neck in them.