He's a new actor to the franchise. So he's either:
A) Replacing an actor who has died.
B) Replacing an actor who is not age appropriate.
C) Playing an established film character who has never actually appeared in them.
D) Deputing an entirely new character as far as the films are concerned.
My money is on D at this point. On it's face, it seems the most probable.
It's also clear he has a ship. He's in the cockpit in space in
thispicture, which looks like it would be the cockpit of the ship parked at the AT-AT shack in
thisstill shot, based on the support framing. It makes me wonder why Han would have to go to Tatooine to take all of them to Yavin, as the source claimed.