Matthew Poole and continuators on 1 Samuel 17:33

33 And Saul said to David, Thou art not able to go against this Philistine to sight with him: for thou art but a youth , and he a man of war from his youth.

Either, 1. For Age, to wit, comparatively to Goliah, being now not much above 20 years old, as is supposed. Or rather, 2. For Military skill, as the words following explain it; as if he should say, Thou art but a Novice, a raw and unexperienced Souldier, and therefore unable to Fight with him.