Matthew Henry Presbyterian @wholebiblehenry

We have here the anointing of Jehu to be king, who was, at this time, a commander (probably commander-in-chief) of the forces employed at Ramoth-Gilead, Kg2 9:14. There he was fighting for the king his master, but received orders from a higher king to fight against him.

Commenting on 2 Kings 9:1-10

John Gill Reformed Baptist @doctorgill

So the young man, even the young man the prophet, went to Ramothgilead. It is repeated, that it might be observed that it was a young man that went, who was more fit for this service than Elisha, partly because of his age, and partly because he would be less known; as also his age is remarked, this being a bold and daring action in...

Jamieson-Fausset-Brown Reformed @jfbcommentary

So the young man . . . went to Ramoth-gilead--His ready undertaking of this delicate and hazardous mission was an eminent proof of his piety and obedience. The act of anointing being done through a commissioned prophet, was a divine intimation of his investiture with the sovereign power.