Goliath’s sword – the one David used to cut off Goliath’s head was probably a Canaanite sword, taken as a battle trophy by Goliath, because tradition states that the Sword of Goliath was curved. It could also have looked similar to the standard Philistine sword. The Bible doesn’t provide much information about the sword, probably because it was not Goliath’s offensive weapon of choice. He apparently preferred the spear. The sword was probably about 2 feet long and weighted between 1.5 and 2.5 pounds. The handle was probably wood inlayed for the Canaanite sword and wood overlaid for the Philistine sword. The curved blade of the Canaanite sword created more downward trust and damage, and was used as a slashing sword, while the straight blade Philistine sword was for both slashing and thrusting. Either one would wreck your day if it struck you. Regardless of the type of sword used, David could easily cut Goliath’s head off with it.
David – prior to becoming King was “ruddy” or red headed, attractive and probably fair skinned for an Israelite (1 Samuel 16:12). He was anointed by Samuel in his early teens, probably 13-15. Three of his brothers were in King Saul’s military and you could not serve unless you were at least 20 years old and David was the youngest of 8 sons. Since we don’t know the ages of his military serving brothers, we cannot know David’s actual age. When anointed, David was filled with the Spirit of the Lord and the Spirit left King Saul. Because of this, Saul was afflicted, and wanted someone to play the harp to sooth him (possible clinical depression). David was a great harp player and a mighty valiant man or war (Samuel 16:18). By this time he had killed a bear and lion while guarding his father’s sheep and was considered a mighty man or war, so by this time he was probably in the military. This would lead me to believe that he was probably 20 years old when he faced Goliath. Since he was the youngest son of Jesse, he was probably chosen to stay home and tend the flocks and didn’t return to the battle front until he found out all of Israel’s army was afraid of Goliath.
David was a red headed, fare skinned, shepherd, musician and mighty man of valor that faced a man at least 3 feet taller than himself with a sling and 5 smooth stones. David’s sling was an Israelite weapon. A good Slinger could hurl a 2-2.5 inch in diameter stone more than 400 yards (Judges 20:16). It was a serious weapon of war, constructed of woven animal hair. http://www.christiananswers.net/q-abr/abr-slingsforkids.html