This age thing is so overrated. Old school players like Stockton went to college for 4 years before being drafted. Yes, high school players are more advanced; they play a much more robust schedule outside of HS than players in the previous eras of basketball. So 1-and-done rookies might be at an advanced skill level than previous generations. But to think Mitchell can't make huge leaps is also erroneous. Just look at Hayward at 21 (couple of years in the league) vs. what he is today. Or George Hill. Mitchell committed late to basketball. And his work ethic is going to carry him a long ways. I think he eats up everything Quin teaches him. Wouldn't surprise me one bit if he's getting major rotation minutes very early.
I didn't say he can't make huge leaps. I just said statistically it's not that likely and advised to avoid unrealistic expectations since the names Westbrook and Wade were mentioned. Maybe starting late means his learning curve is steeper right now, we'll see how long that keeps that way.