The name originated in Toshiyori (literally, old persons), which was an important post in the Tokugawa clan when the Tokugawa family was a daimyo, and the use of Roju for the post was established in around the Kanei era (1624 - 1644).
大名時代の徳川氏の年寄に由来し、寛永ごろに老中の名称が定着した。