Genesis 35:28

And the days of Isaac were an hundred and fourscore years.

Isaac's lifespan is recorded as 180 years. He lived many years after bestowing the blessing on Jacob. During those later years the conduct of Esau and of Jacob convinced him that the blessing rightly belonged to Jacob. Since Jacob and Esau were 120 when he died, he lived long enough to pass on to them the knowledge of what God had taught the earlier generations. His age helps show how that knowledge could be handed down directly from Adam through Methuselah, Shem, and Abraham, then through him to Jacob, the father of Israel's tribes.