There is no gun that well suits a 6-year old that will equally well suit a 26-year old.
So, is the kid going big-game hunting now, or are you just jumping ahead in your purchases?
For immediate use, get him a Handi-Rifle with either a 30-30 or 357Mag barrel. He'll keep it around his whole life just for nostalgia.
For future use, get him a pre-64 Win70 Featherweight in 270 or 30-06. He'll keep it around his whole life for the pride of ownership and usefulness.
All else is simply you projecting your own fantasies onto your kid. Let him make his own choice when he's ready.
