Your college roommate was born in war-torn cambodia and immigrated to america at the age of 2. Trying to understand his life, you ask him what it was like in cambodia. In response, he says he only knows what he has been told by his older brothers and sisters and cannot remember anything himself. You are not worried by his amnesic state because it is common for individuals not to recall the first few years of life due to infantile amnesia. What is clear is that your roommate's siblings are older than he is and can recall their time in cambodia. In regard to brain development and the encoding and retrieval of long-term memories, your roommate's siblings are at least ______ years older than he.