If you're feeling like time is running out in your race to do something significant with your life, consider the example of Caleb.
The children of Israel had escaped from slavery in Egypt, seen the pursuing army drowned in the Red Sea (that they had just walked across the dried bed of), and were standing at the brink of the Promised Land. Representatives from each of the 12 tribes were sent in to scope out the place.
Joshua and Caleb were the only two who came back saying, "This is a great place! Let's go in and take over what God has promised to give us!" The other 10 were all "This is a great place! There's no way we can defeat the current inhabitants!"
Fast forward: After wandering around the desert 45 years, partly as punishment for their lack of faith, partly as a training ground for trusting in Yahweh, the nomads are once again preparing to take possession of the land. Caleb speaks: "I was forty years old when Moses the servant of the Lord sent me from Kadesh Barnea to explore the land. And I brought him back a report according to my convictions, but my fellow Israelites who went up with me made the hearts of the people melt in fear. I, however, followed the Lord my God wholeheartedly. So on that day Moses swore to me, ‘The land on which your feet have walked will be your inheritance and that of your children forever, because you have followed the Lord my God wholeheartedly.’
“Now then, just as the Lord promised, he has kept me alive for forty-five years since the time he said this to Moses, while Israel moved about in the wilderness. So here I am today, eighty-five years old! I am still as strong today as the day Moses sent me out; I’m just as vigorous to go out to battle now as I was then. Now give me this mountain that the Lord promised me that day. You yourself heard then that the Anakites were there and their cities were large and fortified, but, the Lord helping me, I will drive them out just as he said.” (Joshua 14:7-12)
In other words, because he was trusting in God to do what God had promised, this 85-year-old man looked giants in the face and said, "Bring it!"
For non-Biblical examples of those who arrived at greatness later in life, take a minute and a half to look at this video by Tadas Vidmantas.
Truth is...there's a flip side to this. None of us are guaranteed to wake up tomorrow. So yeah, make plans and try to have your life make a positive difference, but hold lightly to the things of this world and find some way to serve and something to enjoy in each day.