The Bible does not specifically say how old he was but it does call him a "youth," which probably means about 12-16 years old.
David did not kill Goliath in a city, but rather in a field known as the Valley of Elah.
Goliath.
There is more than referance to Goliath in the Bible, but the main story of David and Goliath is found in 1 Samuel 17.
Goliath
1 Samuel 17(NIV Version I'm not sure about the others)
Goliath was the giant who fought against a young King David in the Old Testament of the Bible. Goliath's mother was David's mother's sister in law, Orpah.
Goliath was a Philistine. (Specfically, he was from the city of Gath, a Philistine city-state.)
Goliath is played by nelson who is voiced by Nancy Cartwright.
1 Chronicles 20:5 lists Lahmi the brother of Goliath. 2 Samuel 21:19 records the death of "the brother of Goliath," but does not give a name. There are no other mentions of brothers of Goliath in the KJV bible. Although, the bible does speak about Goliath having four sons. (2 Samuel 21:22) "These four were born to the giant in Gath..."
Oh, dude, Goliath was like super old when he died. He was around 40 years old, which is like ancient in giant years. Can you imagine being a 40-year-old giant? Like, that's practically retirement age in giant terms.
The Bible doesn't say.