Which developmental psychologist believed that the period between the ages of 45 and 55 is important regarding "keeping the meaning" versus rigidity?

The correct answer is Vaillant.

George Eman Vaillant is a psychologist who majored in developmental psychology. He is most interested in how children develop into adults, and later on how adults cope with getting older and older. One of his major studies is about 'keeping the meaning' of life, where he believes that we need to work on that, especially between the ages of 45 and 55, which are critical ages.