Speaking as a 45-year-old - your body will be just as capable 15 years from now. But I would hope that over the course of those 15 years you'd learn that if yo

Speaking as a 45-year-old - your body will be just as capable 15 years from now. But I would hope that over the course of those 15 years you'd learn that if you've been working 12 hours a day for four years and haven't gotten done what you want to do, you're doing it wrong. (Sorry if that sounds too harsh.) At the risk of going cliché, sometimes you really do have to work smarter, not harder. Analyze what those 12 hours are, and eliminate or delegate whatever you can. And get some sleep. Now excuse me, I have about 15 hours of work ahead of me today, so do as I say, not as I do.