1 Samuel 17:33

And Saul said to David, thou art not able to go against this Philistine to fight with him,.... Had neither strength of body, nor skill in military affairs, to encounter with a man of his stature, and warlike genius and practice:

for thou [art but] a youth; some say about fourteen or sixteen years of age, but very probably about twenty, and not more, and so not only weak, but inexpert in the art of fighting:

and he a man of war from his youth; a gigantic man, trained up in, inured to, and expert in the affairs of war; so that David could not, on any account, be a competitor with him, and a match for him.