Matteo Tonello
Matteo Tonello

CEOs have been riding the bull market, according to a report by The Conference Board, but the times in the c-suite may soon be a 'changin.'

The "CEO Succession Practice: 2018 Edition" study finds the average age of a chief at an S&P 500 company is 58.3 years old, more than two years old than the average age in 2009.

Nearly 17% of sitting CEOs reached retirement age (64 or older) in 2017, which is the highest level since TBC began tracking succession.

Compiled with Heidrick & Stuggles, TCB report finds that CEO tenure has hit 11 years, the highest since 2002.

It found a widening gap between CEO exits from better-performing and under-performing companies.

The succession rate at the better-peformers clocked in at 6.8 percent, compared to 22.1 percent at under-achievers.

“Our findings suggest that a new generational change in the top business leadership may be underway," Matteo Tonello, TCB's managing director of corporate leadership, said in a statement. "Boards of directors should therefore be aware of the possible increase in demand for top talent and have a sound CEO succession plan in place to retain a competitive advantage over their peers.”

He wrote the report with Jason Schloetzer, professor at Georgetown's McDonough School of Business.

The study also found that gender diversity is an elusive goal for the largest companies.

Women headed 27 S&P 500 companies in 2017, up from 26 in 2016.

The report notes that if the rate of increase in female CEOs were to continue at the 2001-2017 level, there would be fewer than 100 women CEOs of S&P 500 companies in 2034.