If Mahomes finishes with the perfect 158.3 passer rating he has now, only three QBs under age 23 have accomplished the same feat:
Robert Griffin, 2012, 14-15, 200 yards, 4 TD
Marcus Mariotta 2015, 13-15, 209, 4
Drew Bledsoe 1993, 9-11, 2
Mahomes now: 20-23, 309, 6