Life extension

He changed the subject. "How old are you really, anyway?"

"One hundred and twenty."

His eyebrows went up. "An unusual age to go on travels."

"Well... After living a normal human lifespan, I figured it was time to do something risky for a change. Got my wish, too."

"You mean two human lifespans."

Oh, right.

"Slip of the tongue," I said quickly.

...

Son, he says. I tried not to think that without access to modern medicine I was going to grow old and die like any of them. I had, what, forty years left? Sounds like a lot, until one day you look at the calendar and the decades have all but elapsed.

— Little Magic.

Human beings have always dreamed of defeating death, and space age medicine has come a long way towards achieving this dream. A blend of medication and short-lived nanobots, administered over several months, can revert a person's biological age to as low as 17 years. That can't be done more often than every few years, and indeed only affluent people can afford to do it that often, but it can be repeated indefinitely. Effectively, people in this age only die of accidents or the odd disease that still lacks a cure. But that means life remains dangerous enough, especially in space, leaving people far from immortal. Doubly so as mind upload is inherently unreliable, and few people can adapt to life on a digital substrate.