Albert Barnes Commentary Job 15:10

"With us are both the gray-headed and the very aged men, Much elder than thy father." — Job 15:10 (ASV)

With us are both the gray headed - That is, some of us who are here are much older than your father; or we express the sentiments of such aged men. Job had admitted (Job 12:12) that with the aged was wisdom, and in length of days understanding; and Eliphaz here urges that on that principle he and his friends had a claim to be heard. It would seem from this that Job was very far from being regarded as an old man and would probably be esteemed as in middle life. The Targum (Chaldee) refers this to Eliphaz himself and his two friends: “Truly Eliphaz, who is hoary-headed (דסיב) and Bildad, the long-lived (דקשיש) are with us, and Zophar, who is older than your father.” But it is not certain that he meant to confine the remark to them.

It seems to me probable that this whole discussion occurred in the presence of others, and perhaps was a public contest. It is clear, I think, that Elihu was present and heard it all , and it would accord well with Oriental habits to suppose that this was a contest of skill, which many were permitted to witness, and which was continued for a considerable time. Eliphaz may, therefore, have meant to say that among his friends who had assembled to hear this debate, there were quite a few who shared his opinion, who were much more aged than Job, and who had had much longer experience in the world.