I found this helpful summary on the idea of τέλειος (commonly translated as “perfect”) in the Old Testament. Taken from Paul DuPlessis – Τέλειος: The Idea of Perfection in the New Testament (101–102):
It is a totalitarian motive centred in the consciousness of a divine relationship between God and the people of His choice. Whether they are described as “perfect”, “righteous”, “holy”, or “pure”, these attributes go back to the same source and are of kindred character. Only in this sphere of religious truth is it possible to arrive at an impression of O.T. perfection. For the Hebrew it was not an abstract quality or the static summit of endeavor by knowledge and reflection. It consisted of activity, formed a way to be walked and created a dynamic piety governing all outlets of human existence. Such a man was bound by considerations of striving to be in accordance with what he should be in the eyes of Yahweh, Who is holy and pure and Who is Himself the image of what He commands. If a man is firmly rooted in this relationship, he is “whole”, “sound”, “complete”, “perfect.” Thus the safety of the community is secured by the firm grip of an unfettered alliance. Men of this stamp were Noah, Abraham, Joshua, David, Solomon, and others. For all they failings they excelled in unity of heart, and treaded the trail blazed by the commands of Yahweh.