Intergenerational friendship “enriches us and gives us a sense of connection that is life-affirming and energizing,” said Marc Schulz, a professor of psychology at Bryn Mawr College and co-author of the book “The Good Life,” who has studied how important personal relationships are to happiness. In general, younger friends rely on their older friends for guidance, though the reverse is true, too. Dr. Schulz noted that the college students he has taught for three decades keep him “young” and “invigorated.”