You can't stop aging. Gene therapies and replacement organs and plastic surgery give it a good fight. But it catches up with you anyway. Get a new lung, and your heart blows a valve. Get a new heart, and your liver swells up to the size of an inflatable kiddie pool. Change out your liver, a stroke gives you a whack. That's aging's trump card; they still can't replace brains.

Life expectancy climbed up near the ninety-year mark a while back, and that's where it's been ever since. We eked out almost another score from the "three score and ten" and then God seems to have put his foot down. People can live longer, and do live longer—but they still live those years as an old person. Nothing much has ever changed about that.

Look, you: When you're twenty-five, thirty-five, forty-five or even fifty-five, you can still feel good about your chances to take on the world. When you're sixty-five and your body is looking down the road at imminent physical ruin, these mysterious "medical, surgical and therapeutic regimens and procedures" begin to sound interesting. Then you're seventy-five, friends are dead, and you've replaced at least one major organ; you have to pee four times a night, and you can't go up a flight of stairs without being a little winded—and you're told you're in pretty good shape for your age.

Trading that in for a decade of fresh life in a combat zone begins to look like a hell of a bargain. Especially because if you don't, in a decade you'll be eighty-five, and then the only difference between you and a raisin will be that while you're both wrinkled and without a prostate, the raisin never had a prostate to begin with.

So how does the CDF manage to reverse the flow of aging? No one down here knows. Earthside scientists can't explain how they do it, and can't replicate their successes, though it's not for the lack of trying. The CDF doesn't operate on-planet, so you can't ask a CDF veteran. However, the CDF only recruits on-planet, so the colonists don't know, either, even if you could ask them, which you can't. Whatever therapies the CDF performs are done off-world, in the CDF's own authority zones, away from the purview of global and national governments. So no help from Uncle Sam or anyone else.