It wasn't Lee's age
We finally got some official insight into why Lee Bienstock was fired and Sean Yazbeck was hired.
From Trump University's "Lessons Learned":
What can we learn from this season?It would have been nice if Trump had articulated these reasons at the final boardroom, but - at that time - he didn't provide any explanation for firing Lee and hiring Sean. The past few days there has been discussion of the fairness of selecting young candidates for the competition if their age prevents them from being hired. The statement above may be an attempt to address that issue.
Sean and Lee are both excellent leaders. But in the end, Sean's greater maturity made him this season's Apprentice. Remember, maturity is not a question of age. It comes from a winning attitude, enlightened leadership, attention to detail and the other traits we saw in Sean throughout this season.