[cypher]

6 days isn't long at all so you've been doing well with him, don't stop & leave him now as that will just set things back, be patient but consistent.
It's a little difficult to tell if this is him being territorial or just normal nibbling behaviour, they do tend to nibble a bit at first as they work out where food stops & hands begin & it's a way of exploring new things.
Rushing over to bite does sound more like him being territorial though.
Try not putting your hand in the cage for a little while (you can do food & water when he's sleeping) & just interact with him out of the cage.
Use a mug, tube or anything he'll happily climb into that you can safely transport him in then set up a safe play area, it could be a large plastic storage bin with some of his substrate & toys in or a playpen, bought or made, again with a few toys, hideouts & a wheel.
Give him a little time to run around & explore once you've taken him to the play area then try interacting with him, if it is him being territorial then the biting should stop although you may still get some exploratory nibbles for a while.