In Walter Isaacson's biography of Steve Jobs, he recounts Jobs' early days at Apple and his intensity which led both to creating great products and to sometimes treating people harshly. Isaacson tells this story:
Jobs confided in [John] Sculley that he believed he would die young, and therefore he needed to accomplish things quickly so that he would make his mark on Silicon Valley history. "We all have a short period of time on this earth," he told the Sculleys as they sat around the table that morning. "We probably only have the opportunity to do a few things really great and do them well. None of us has any idea how long we're going to be here, nor do I, but my feeling is I've got to accomplish a lot of these things while I'm young."
Regardless of when you accomplish something - at 18 or 80 - you will probably only be able to accomplish a few great things in your lifetime. I mean really great things. This is because great things take time and effort. They take attention to detail. They take becoming great - better than anyone else, even - at something.
And, since you don't know how long you'll be here, focus on the things that really matter to you - your passions, gifts, and talents. Hone them. Perfect them. Get great at them. And then watch as your strengths allow you to make your mark, however long on the earth that may be.