How old was Abraham when he married Keturah?

According to the Genesis account, Abraham was 150 years old when he married Keturah, several years after Sarah's death. Scripture notes his life span divides by fives: called from Ur at 50, into Canaan at 75, Isaac at 100, Keturah at 150, and death at 175.

Les explains that Sarah had died and several years later, probably about ten years, Abraham married Keturah. He bases this on Genesis 25:1, saying that as near as he can tell from figuring the time, Abraham was 150 years old. Les points out Abraham's life span divides by fives—called out of Ur at 50, commanded into Canaan at 75, Isaac born at 100, Keturah at 150, and death at 175—showing him as the epitome of God's grace.

Genesis 25:1

Then again Abraham took a wife, and her name was Keturah.