On the left is a male, on the right is a female. Females only have green color on necks, young boys can have both blue and green. Plus these are old enough for the boys to show distinct barring all over his wings and back while the girls rapidly lose them, becoming solid colored over the same areas(mud brown).
It takes the males three years to attain full plumage. The male in picture is a year old or less. Next year, his neck and chest will be more evenly colored, how much green he will have on back and tail will be a total guess, it varies wildly between two year old boys.