Roger Cohen joined The New York Times in 1990. He was a foreign correspondent for more than a decade before becoming acting foreign editor on September 11, 2001, and foreign editor six months later.

Since 2004 he has written a column for the Times-owned International Herald Tribune, first for the news pages and then, since 2007, for the Op-Ed page. In 2009 he was named a columnist of The New York Times.

Mr. Cohen has written "Hearts Grown Brutal: Sagas of Sarajevo" (Random House, 1998), an account of the wars of Yugoslavia’s destruction, and "Soldiers and Slaves: American POWs Trapped by the Nazis Final Gamble" (Alfred A. Knopf, 2005). He has also cowritten a biography of General Norman Schwarzkopf, "In the Eye of the Storm" (Farrar Straus & Giroux, 1991).

LONDON — It does not seem that long ago that the Beatles could plausibly portray geriatric redundancy as beginning at an age sometimes referred to as young these days. “Will you still need me,” they asked, “Will you still feed me, when I’m sixty-four?”That was, in fact, a while back — in 1967. But such is the mist cast by advancing years that it is hard to believe we stand close to a half-century from the Sgt. Pepper’s Lonely Hearts Club Band album. Since then life spans have grown dramatically in an acceleration of the process that has seen longevity double in developed countries over the past 150 years. In 1850, half of England’s population was dead by 45. Today, according to Sarah Harper, a British gerontologist, half the English population is alive at 85.

But these advances brought on by antibiotics, vaccination programs, improved sanitation and better medicine (not to mention dietary supplements and the treadmill) are peanuts compared to what may lie in store. The brave new world of regenerative medicine is upon us. This is the term of art for the various techniques and technologies (including cell therapy, gene therapy and tissue engineering) that will, its advocates say, allow the body to slow, halt or even reverse aging by enabling the regeneration and repair of damaged organs, cells and tissues. Talk of routinely living to 120 or even 200 no longer lies in the realm of cranks and fantasists.

Indeed, the buzz around radical life extension is such that the dot-com gurus who brought us the likes of Google and PayPal now find themselves laser-focused on an Age of Longevity, as if transforming our lives was not enough whereas doubling them through moonshot thinking would be an incontrovertible contribution to human progress. Connectivity was O.K., but conjuring super-centenarians will be better. Larry Page, the chief executive of Google, and Peter Thiel, the Silicon Valley billionaire, early investor in Facebook and co-founder of PayPal, are among those who, in separate ventures, have aging in their cross hairs.

“If people think they are going to die, it is demotivating,” Thiel told me. “The idea of immortality is motivational.” He described his ideas as “180 degrees the opposite” of Steve Jobs’s, who once said: “Remembering that you are going to die is the best way I know to avoid the trap of thinking you have something to lose. You are already naked. There is no reason not to follow your heart.”It is probably wise to take Thiel’s idea of an end to aging (or at least its radical postponement) seriously. Any extrapolation from technological progress over the past quarter-century makes the notion plausible. At least seriously enough to ask the question: Do we want this Shangri-La? Do we want a world of boomerang generations where, like Prince Charles still awaiting his big job, we’ll be lucky to come into an inheritance at 80?More seriously, given limited natural resources, already aging populations, spreading megacities, a dearth of jobs in the developed world, severe strains on health services, disappearing pensions and growing inequality, the idea of radically extending life (initially for the rich, one assumes) seems ominous — even if human adaptability and ingenuity are always underestimated.

Then there are the deeper moral issues. Nature can, of course, be improved upon or we would still be dying of polio. But it would be rash to imagine that tampering to this degree with our human lot and altering so radically the delicate equilibrium of humankind and nature will not produce plenty of Donald Rumsfeld’s “unknown unknowns,” deathless monsters of our own creation. Radical life extension smacks of an intemperate claim to have unlocked the fundamental mystery of life. That is dangerous territory.

This year, the Pew Research Center found that in the United States, where current life expectancy is 78.7 years, 56 percent of American adults said they would not choose to undergo medical treatments to live to 120 or more. Their median ideal life span was 90. A small majority said radical life extension would be bad for society. Americans, it seems, are ready to wear their trousers rolled rather than be seduced by eternal youth.

This resistance to the super-centenarian dream demonstrates good sense. Immortality — how tempting, how appalling! What a suffocating trick on the young! Death is feared, but it is death that makes time a living thing. Without it life becomes a featureless expanse. I fear death, up to a point, but would fear life without end far more: All those people to see over and over again, worse than Twitter with limitless characters. As Martin Amis has observed, “I find that in your 60s everything begins to look sort of slightly magical again. And it’s imbued with a kind of leave-taking resonance.”Memento Mori is perhaps life’s greatest spur. And, as Christmas Day reminds us, you can do a lot by the age of 33.