When does a mallard male get a green head?

[Stormdog]

My mallard is getting some very vibrant coloring in the feathers... Lots of blue and white in the wings. Also has a dark crest, like a mohawk, but this has started looking a very deep green-ish cast in the sun.

If this is a male, when can I expect the full green head?

 

[xfilesnumber1fan]

My mallards green heads were the last to come in as far as colors go..They were 16 to 20 weeks they had their full green heads...