How old was david when he faced goliath?

Answer 1

According to Numbers 1:2-4 (AMP):

2 Take a census of all the males of the congregation of the Israelites by families, by their fathers' houses, according to the number of names, head by head

3 From twenty years old and upward, all in Israel who are able to go forth to war you and Aaron shall number, company by company.

4 And with you there shall be a man (to assist you) from each tribe, each being the head of his father's house.

You had to be 20 years old to fight in the army. David was the youngest of 8.

He went and visited his 3 older brothers...

1 Samuel 17:12-16 - 12Now David was the son of an Ephrathite of Bethlehem in Judah, named Jesse, who had eight sons. In the days of Saul the man was already old and advanced in years. 13The three oldest sons of Jesse had followed Saul to the battle. And the names of his three sons who went to the battle were Eliab the firstborn, and next to him Abinadab, and the third Shammah. 14David was the youngest. The three eldest followed Saul, 15but David went back and forth from Saul to feed his father's sheep at Bethlehem. 16For forty days the Philistine came forward and took his stand, morning and evening.

That means three of the sons were over 20 and five of the sons were under 20, including David. Perhaps the fourth son was 19, the fifth son was 18, the sixth son was 17, the seventh son was 16, David has to be at the most, 15, and most likely younger than 15 as having a baby every year was probably unlikely.

Answer 2

he was about 15 years of age when he faced goliath

Answer 3

12