Keith Paul Bishop writes:
A recent study by four professors finds quite a few faults with older directors:
"Specifically, older independent directors are more likely to miss board meetings and less likely to be a member or chair of important board committees. Their presence on corporate boards is associated with higher CEO compensation, poorer financial disclosure, lower total payouts, worse acquisition decisions, and a lower sensitivity of CEO turnover to performance. On average, a greater representation of older independent directors on corporate boards is negatively related to firm performance."
Ronald W. Masulis, Cong Wang, Fei Xie & Shuran Zhang, Directors: Older and Wiser, or Too Old to Govern? (Dec. 2018, available here). The authors do allow that these negative impacts are somewhat offset by advisory benefits but one can almost hear Regan counseling her father:
"O, sir, you are old!
Nature in you stands on the very verge
Of her confine. You should be rul'd, and led
By some discretion that discerns your state
Better than you yourself."
W. Shakespeare, King Lear Act II, sc. 4 (matters do not end well for Regan).
The authors classify anyone who is at least 65 to be "older".