You could be the world’s fittest person and yet be struck by an on-coming car and be dead. Your life is in God’s hands entirely. So, if we want to live long, we must give God a reason to do so. Listen to my argument… 
How have you experienced God to tell your children? Do you have some amazing stories to tell your children to inspire them to follow God? Even if you are single now, is God working in your life in such a way that you will have many stories to tell to your future children? 
So even to old age and gray hairs,O God, do not forsake me,until I proclaim your might to another generation,your power to all those to come.Ps. 71:18
The psalmist wants to live long until he sees generations of his children. His motivation? So that he can tell them how wonderfully and faithfully God has worked in his life. He wants to be a witness for God to the future generations. If you were God, wouldn’t you listen to such a request? 
If God will allow it, you will one day get old and have gray hairs. When that time comes, wouldn’t it be great if you could tell your children and grand children of how God worked in and through your life to do wondrous things? 
This is something we ought to be praying for. Pray that God will so reveal Himself to us and involve us in His ministry that we will have stories to tell our children and grand children. 
PH