Seasoned executives, particularly the more "senior" ones, are discovering that they actually have a lot to learn from the individual they mentor. Being in the corner office has its advantages, but it also has a tendency to isolate you from many of the important day-to-day aspects of the business.
By spending time listening first-hand to those who are much further down the chain of command, you may find out a lot of things you didn’t know, and not just about your organization. Many new ideas, technologies and problem solving approaches are being identified and developed by young people with a completely different mindset than ours, so it's important to stop teaching now and then and see what you can learn.
The ability to share the benefit of one's experience with an eager mind is usually the draw for mentors, but the reward is almost always the renewal and energy that are returned.