Final answer:
Levinson's theory states that the transition into middle adulthood lasts about five years, a period marked by personal development, aging signs, and health risks.
Step-by-step explanation:
According to Levinson's theory, the transition to middle adulthood lasts about five years. Middle adulthood is a stage that typically spans from the mid-30s to the mid-60s. This is a period when individuals often focus on family, career achievements, and begin to experience signs of aging, such as the appearance of wrinkles and gray hair. Additionally, this life stage sees an increased risk for developing chronic diseases like type 2 diabetes, cardiovascular disease, and cancer.