Genesis 21:5

“So Abram went, as the LORD had told him; and Lot went with him. Abram was seventy-five years old when he set out from Harran.”

Provides context to Abram's age when he initially left Haran.

“Abraham fell facedown; he laughed and said to himself, “Will a son be born to a man a hundred years old? Will Sarah bear a child at the age of ninety?””

Highlights the miraculous nature of Isaac's birth, given Abraham's advanced age.

“Sarah became pregnant and bore a son to Abraham in his old age, at the very time God had promised him.”

Reinforces that Isaac's birth occurred in Abraham's old age, as promised.

“By faith Abraham, even though he was past age—and Sarah herself was barren—was enabled to become a father because he considered him faithful who had made the promise. And so from this one man, and he as good as dead, came descendants as numerous as the stars in the sky and as countless as the sand on the seashore.”

New Testament reflection on Abraham's faith in begetting a child in old age.