Valmiki is the legendary sage who composed the Ramayana, which dates back to a much earlier period than the Gupta Golden Age (circa 4th to 6th century CE). Scholars like Aryabhatta, Varahamihira, and Nagarjuna are famously associated with the scientific and philosophical advancements of the Gupta era. Therefore, Valmiki is the correct choice as he does not belong to this period.