Final answer:
Cast syndrome primarily affects individuals in body casts due to prolonged immobilization in a supine position, which can lead to duodenal compression.
Step-by-step explanation:
The group of people most commonly associated with cast syndrome are individuals in body casts. Cast syndrome, also known as superior mesenteric artery syndrome, is a potentially life-threatening condition that occurs when a person in a body cast develops duodenal compression between two arteries. This typically happens when the body is in a prolonged supine (lying down) position, as can be the case with extensive spinal or orthopedic casts. While not exclusive to any specific age group, it is the immobilization and the type of cast that are the key factors leading to this syndrome, rather than the age of the individual.