Job 14:1-6 and Psalm 139:16 teach us that God has determined and numbered our days before we were born. In other words, God knows exactly when we’re going to die, which begs the question, “Is there anything we can do to change or prolong that date?”
I believe there is and I’m slightly dogmatic about it because God has said that if we walk in obedience and keep His decrees and commands, He will give us a long life (1 Kings 3:14) and if we honor our parents, we may live long in the land (Ex 20:12). When we consider that God is omniscient, knowing the beginning from the end, we can trust that He has factored in our obedience, or lack thereof, before He chiseled our obit day in stone.
Taking it a step further I believe we can prolong our lives if we stop smoking, doing drugs, and abusing alcohol, and start exercising, 
eating right, and taking care of our bodies, because God, again knowing all future events, has factored in both our harmful and beneficial behaviors, before we were born. That is to say, our favorable activities and obedience to God are not merely things that may improve the quality of life in the time we have been allotted, but rather things that God has considered in determining the length of our lives.
eating right, and taking care of our bodies, because God, again knowing all future events, has factored in both our harmful and beneficial behaviors, before we were born. That is to say, our favorable activities and obedience to God are not merely things that may improve the quality of life in the time we have been allotted, but rather things that God has considered in determining the length of our lives.
Of course we must also remember that God considers things we know nothing about that may result in a long or short life, and Godly obedience and healthy living are not the sole factors that decide how long we live.
He Dwells -- The B'log in My Eye 