David was barely a teenager when he fought Goliath is a Myth, although he is shown in many illustrations as very young. That comes from the Latin text which calls David a child, a miss-translation of the Hebrew, which calls him a young man. David was at least twenty-seven, maybe twenty-eight, when he fought Goliath. The key to David’s age is the two years of Saul’s reign and the seven and a half years that David was king over Judah while he was in Hebron. David was thirty when he began his reign in Hebron, which came immediately after Saul’s two-year reign. (See 1 Samuel 13:1. See Timeline in Hebrew Texts.)