Let's play the mystery player game.
Player #1:
Age: 19
MPG: 32.2
FG%: .427
3P%: .327
3P: 2.3
FT%: .713
RPG: 7.8
APG: 6.0
STL: 1.1
BLK: 0.3
TOV 3.4
PTS: 21.2
These are the per-game stats put up by none other than the 2018-2019 ROY, #3 overall pick Luka Doncic. It's pretty amazing what he did as a rookie - it's pretty special.
Just cherry picking some stats, but Knox had a better FT% (.717) and 3p% (.343)
Or how about these:
Player #2:
Age: 19
MPG: 39.5
FG%: .417
3P%: .290
3P: 0.8
FT%: .754
RPG: 5.5
APG: 5.9
STL: 1.6
BLK: 0.7
TOV 3.5
PTS: 20.9
Player #2 is none other than Lebron James.
It's interesting that James had a very solid FT% as a rookie (career .736; last season .665), but relatively poor 3pt% (career .343).
What's notable to me is that the Cavs played teenage Lebron a whopping 39.5mpg - seems a bit cruel straight out of high school.
These were 2 of the more exceptional rookie stat lines (especially for 19 year olds) in the history of the NBA. Usage is a bit of a funny thing to predict - while it's largely predicated on team depth, few players are capable of handling the load.
Barrett might be one of the rare players that might be capable of approaching these numbers.