It is interesting that after acknowledging that he is young and should not presumptuously judge one of his elders, Elihu jumps in and does just that. It's also interesting that Job does not answer Elihu. Neither does God. It seems to me that the 'ignore' treatment is a devastating way of putting an impudent young man in his place. He is irrelevant. He may or may not be speaking truth, but he has no place to speak in judgment of a man his elder and his superior in every way. Even if everything he says is true, he has not earned the right to speak condemnation or correction to Job, because he has never proved himself in his own character or righteous actions, neither has he suffered as Job. Moreover, he has no authority to speak in anger against these men, his elders.
We can safely assume that Job's friends were counted as friends and equals by him. Job knew many people and was good to all, but not a friend of all. To be a man's friend, one must be his equal. His friends had a right to try to help Job sort out theologically why these things were happening to him. The fact that they assumed he must have sinned simply reflects the theology they all believed at that time. Job, himself, couldn't understand precisely because he, too, believed that God, being righteous, rewarded good and punished evil. Yet one thing he did know, he had no guilty conscience about anything he had done. He was trying to re-think his understanding about God's ways, because nothing added up. His friends, however, had no such assurance about Job's sinlessness, despite his steadfast claims. Their lack of compassion for Job, as he bitterly reflected, made them miserable friends.
It is interesting that Job's final response to God was, in effect, saying, "I need to forget about being entitled to Your kindness and rewards because now I have seen You, I realise I am of no account. I deeply regret being so presumptuous to speak." Yet he never conceded he had sinned in any way. His own righteousness had just become irrelevant in light of the magnificence of God.
Two other points are interesting. Firstly, God decreed that it was Job who had spoken rightly of God, while his friends hadn't (and God was angry with them and was prepared to deal harshly with them if Job didn't intercede for them). We need to think about that point. And finally, God, speaking through the prophet Ezekiel hundreds of years later, specified only three men righteous enough to be excluded from God's wrath in a time of judgment - Noah, Daniel and Job (Ezekiel 14: 14, 16, 18, 20). If Job had sinned at any stage during his time of testing, God would not have confirmed his righteousness.
Certainly, Elihu, together with Job's three friends, was incorrect in any accusation against Job. God rebuked Job's friends, but totally ignored Elihu.