Just for comparison, here are Lamar Jackson's junior stats at Boynton Beach:
43% completion, 1,264 yards, 19 TDs and 6 picks. 960 yards rushing and 10 TDs.
And here are Jacurri Brown's junior stats:
48% completion, 1,537 yards, 14 TDs and 7 picks. 1,108 yards rushing and 16 TDs.
To be clear: this does NOT mean Brown will develop like Lamar, Cam and Allen. Those guys are outliers. But there is a history of highly athletic QBs developing their passing skills at a later age. The key is going to be coachability and work ethic. The three NFL guys had that. I don't know anything about Brown in that regard.