The answer is: 90

Gen 17:17 / 21:5

In the grand narrative of Genesis, Sarah’s age when she gave birth to Isaac, 90 years old, might seem striking, but it's a beautiful testament to the miraculous beginnings of Isaac's life—a sign of divine promise and miraculous deliverance. Sarah's journey didn't just stop with her laughing disbelief at the news of her impending motherhood (which really shows her human side), but she ultimately embraced her role, becoming a matriarch of a significant lineage.

Interesting trivia: Sarah, originally named Sarai, faced a long and winding road before mothering Isaac. Her story is woven with themes of faith, patience, and a touch of humor, many of which echo throughout scripture. For instance, Isaac’s birth mirrors Hannah's later experience (1 Samuel 1) with a child born despite her barren state—showing that God’s hand is working through seemingly impossible scenarios.

Moreover, some note that women generally bear children much younger in the biblical circus, so Sarah's age stands free against that backdrop. And speaking of archetypes, just think—Sarah herself transforms through this process. She goes from being known as barren and doubt-filled to renown for her quiet strength and faith, convincing many that divine promise doesn't operate under worldly timelines. Each laugh, each challenge faced together with Abraham serves as a rich ground for discussing themes around hope, patience, and the unexpected joy of new beginnings nourishing generations to come. How inspiring it is for all of us!