Ah, that makes sense.
His legs are thin, but some birds are just super slow to mature. Unless it is a transgendered hen, you've got yourself a roo! And sexlink definitely makes sense! If it were a hen, it would most likely be laying already.
That is most definitely a roo. He is not a maran though.
Looks to me like he has BR in him. I wouldn't be surprised if he was a pet quality barred rock.
Marans have whitish grey legs.