At one time, many people in the Western world anticipated retiring in their 50s or 60s. Now, they are embarking on new careers at the very time that they might have previously been expected to begin a life of leisure. Increased longevity and a drive to keep contributing to society have led to what are often referred to as “encore careers” — new endeavors that are often very different from a person’s past experience. Marci Alboher is the author of The Encore Career Handbook: How to Make a Living and a Difference in the Second Half of Life . She is also vice president of Encore.org, a nonprofit that helps millions of people pursue second acts for the greater good. This is not just about reinventing yourself, she says: “ You have to be a part of changing the world for future generations.” Alboher spoke to Stewart Friedman , Wharton practice professor of management and director of the Wharton Work/Life Integration Project , about second — and even third — acts. An edited transcript of the conversation follows.…