1 Samuel 17:14

Now David was the youngest. The three oldest {followed} Saul,

1 Samuel 16:11

Then Samuel said to Jesse, "{Are all the young men here}?" And he said, "The youngest still remains, but look, he [is] shepherding the flock." And Samuel said to Jesse, "Send and bring him, for we cannot {sit down} until he comes here."

Genesis 25:23

And Yahweh said to her, "Two nations [are] in your womb, and two peoples {from birth} shall be divided. And {one people shall be stronger than the other}. And [the] elder shall serve [the] younger."

Treasury of Scripture Knowledge

Summary

And David was the youngest: and the three eldest followed Saul.

Bible References

The youngest

1 Samuel 16:11
Then Samuel said to Jesse, "{Are all the young men here}?" And he said, "The youngest still remains, but look, he [is] shepherding the flock." And Samuel said to Jesse, "Send and bring him, for we cannot {sit down} until he comes here."
Genesis 25:23
And Yahweh said to her, "Two nations [are] in your womb, and two peoples {from birth} shall be divided. And {one people shall be stronger than the other}. And [the] elder shall serve [the] younger."