The correct answer is early adulthood.
According to Erikson's theory of psychosocial development, during early adulthood (ages 20-40 approximately) individuals experience the sixth stage of psychosocial development known as Intimacy versus Isolation. During this stage of development, individuals are concerned about find an appropriate lifelong partner. At this stage of psychosocial development, individuals are also worried that they will be lonely if they fail to find a partner.