Be Careful What You Wish For

Be Careful What You Wish For - Health Checkup: How to Live 100 Years - TIME

You never get over the moment you realize that you're definitely going to die. You're usually a small child when the insight hits, and you usually have a vague idea of what death is, but the first-person epiphany — the "Wait, that's going to happen to me?" experience — changes everything. Your sense of time and its fleeting passage can never go back to what it was before you discovered that you too are on the clock. (Special Report: How to Live 100 Years.)

It's no wonder we spend our whole lives after that trying to add as many rollover minutes as we can, and in the developed world, at least, we've done a pretty good job of it. In 1900, U.S. life expectancy was just 47.3 years. Now — thanks to better medicine, cleaner food and a whole host of health and safety regulations — it's up to 78.1. That's not the best in the world — other healthy, wealthy countries like Japan and Iceland crack the 80-year mark — but it's not bad.