The company I work for has a 70 year old CEO with an equally as old founder that is active in the company. A prior company I worked for had a leader that left after over 30 years with the company. He decided it was time to retire and enjoy life. He passed away within 6 months. He was not yet 60.
People like Steve are driven people. It is not necessarily the money or prestige that drives them. It is the challenge and the desire to succeed. They have to be doing something important with their lives. And I mean important on a large scale, not just family or charity work.
Providing that his health holds out and he is not removed from the job, he will be there until the end. Or, if he does leave on his own, the end will be very near.
Just my opinion.