It is my firm belief that leaders sometimes overstay their welcome. Organizations change and need different kinds of leadership. Sometimes an organization can become overly identified with its leader, rather than its mission, which can jeopardize the organization's stability or sustainability.
There's no doubt about it -- ageism is out there. Older applicants will inevitably run into hidden objections regarding their energy level, their ability and willingness to do the job, their desire (or lack of it) to learn new skills and other unfortunate prejudgments based solely upon age.