Yes, I certainly have, and I suspect most older people have had the same thought. Life is short, and suddenly we wake up one morning and realize it's almost over. The Bible says, "What is your life? You are a mist that appears for a little while and then vanishes" (James 4:14).
Does this mean our lives are useless, or that it doesn't matter how we live? Some people say this is true; like the man in one of Jesus' parables, they say, "Take life easy; eat, drink and be merry" (Luke 12:19). That man thought he had many years of ease and enjoyment ahead of him -- but he didn't. That very night his life was taken from him -- and God called him a fool.
But God has another way for us, and life's greatest joy comes from knowing Him and discovering His plan for our lives. We aren't here by accident; God put each of us here, and He put us here for a purpose. That purpose is to know Him and follow Him -- and then some day enter into His presence in heaven forever. No matter how young or old we are, God wants us to learn to walk with Him every day.
If you have never committed your life to Jesus Christ, I urge you to do so today. The Bible says, "Now is the time of God's favor, now is the day of salvation" (2 Corinthians 6:2). And if you already know Christ, make it your goal to walk with Him and serve Him every day of your life.