Do you have any pics of your boy's wing feathers at 4 months? The wings on that bird are so brown and have so little striping, that is what has me thinking hen. Your boy's neck also looks a bit brighter in color to me.
I wonder if it could possibly be a low % Spalding hen maybe? I sort of want to say male because the defined barring up front but then the farther back the more it fades. I know Spalding hens can get some barring on them. This chick has me confused. I'm trying to remember if there's a way to sex them based on the neck and breast feather structure at this age.