You may be thinking of the psalmist's words in Psalm 90:10: "The length of our days is seventy years—or eighty, if we have the strength."
God wasn't promising that every person would live to be seventy or eighty, however; the psalmist was simply describing our normal human experience. Our times are in God's hands, and for some their journey on earth is much shorter. Jesus was crucified when He was still in His 30s; the first martyr, Stephen, likewise was probably still a young man when he was put to death for his faith (see Acts 7).
The real point the psalmist was making is that no matter who we are, our time on earth is limited, and someday death will overtake us. Death is a reality, and no one evades it—no matter how strong they are or how many years they live: "You sweep men away in the sleep of death" (Psalm 90:5).
But this leads us to two very important questions. First, how should we prepare for death? People may spend years preparing for a career or advancing in their job—and yet never take five minutes to think about eternity and what will happen to them when they die. But when we know Christ, we know this life is not all, and ahead of us is heaven. Have you put your faith in Him?
The other question is this: How should we spend the days God does give us? Will we live for ourselves—or will we live for God? Put Christ first, and make your days count for Him.