At only 39-years-old, Brad Stevens is already one of the best coaches in the NBA. Stevens is an outlier in many aspects of the league.
In the first place, Stevens is currently the fourth youngest active head coach in the NBA and is the only one in this group not to have played in the NBA. The average age of a head coach in the NBA is just above 48-years-old, which puts Stevens well below average.
Another point about Stevens that makes him unique from other coaches is that his path to the NBA was a non-traditional journey.