In Twilight, Billy Black is supposed to be paralysed. How come he can drive if hes in a wheelchair?

Billy doesn't drive, Jacob drives him around. In chapter
twelve of Twilight, Billy and Jacob visit Charlie and Bella. When
they get out of the car, Jacob had been driving Billy around. Charlie, being a police
officer, comments on the fact that Jacob, who is underage, is driving. Jacob counters
with a lie that they get permits early on the reservation. Charlie lets it go, because
Billy says, "I have to get around somehow." Since Billy is in a wheelchair, Jacob drives
him around, even though Jacob doesn't officially have his driver's license
yet.