He's physically not ready yet, when dudes are underweight like that they typically play them 1 position down until their body catches up. Look at Wiggins, he played SG his first year and a half and is now moving to SF, Durant played SG his first year in Seattle and Paul George played SG his first two years. The average NBA SF is around 220lbs, he's got a long way to get to that weight in terms of functional strength, he's going to be a very good player, but just assuming he'll be a 15ppg scorer off the bat & pull down 6rpg despite being so skinny is crazy talk.
I'd expect him to have a similar projection as Paul George, start off slow, maybe even come off the bench and start putting it together as his body catches up to his skill.
PG at the same age, similar build, he didn't put up 12/6 till his second season.