Why does it say "Asher Ye'atzuhu"?
Malbim: This was a new counsel that he did not ask about. He did not want to agree to their request; he only asked about how to dispel them.
Why did he take counsel from the youths?
Malbim: He thought that the elders are haughty to give counsel unlike he wants. The youths would not do so.
Why does it say that they grew up with him?
Malbim: They will not say that he should lower himself in front of the nation.
Why does it say "ha'Omdim Lefanav"?
Radak: He abandoned the counsel of the Zekenim, who stood in front of his father, and took counsel from the youths, who stand in front of him.
Malbim: He made them officers and counselors in conducting the kingship. This matter is relevant also to them! In a limited kingship, also the royal officers are limited. Surely they will seek strategies to keep the kingship unlimited, for their own benefit!