It's pretty common for all feathers to begin showing their gender at six weeks in most breeds. I find twelve weeks is usually for the harder to sex breeds, such as the Polish or Silkie, but it depends on how fast the individual bird is made to mature. Cockerels feather more slowly than pullets at a young age, so you can identity them as young chicks (around a few days old) by seemingly not having a tail when the pullets already have tails, and by the cockerel in question growing wing feathers much more slowly. Again, this depends on what the bird was bred for.
Ultimately, I would say that your bird is a cockerel because of the suspicious red on his feathers and the pointed-looking hackles, but he looks pretty confusing. Can you get a picture of his hackle and saddle feathers on top of something like a sheet of paper?
