Picture two boxes of mice. In one, they slowly muddle around and become heavier and slower. Many start to become ill. Eventually they all die. But while box one becomes a graveyard, box two hosts a party of happily squeaking rodents.

Researchers at Imperial College London have discovered a way to slow the effects of ageing in mice.

They suppressed the geneA gene is the basic unit of heredity. that produces the proteinLarge biomolecules made of up amino acids, which in turn are made up of DNA. interleukin-11.¹ This improved their senses, muscle function and metabolismThe chemical processes within the body which produce energy. It derives from a Greek word meaning "change"., and prevented cancer. It enabled them to live 25% longer lives than untreated mice.²

And it allowed them to keep their glossy dark fur. No more grey hair. No more balding. These mice have been nicknamed "supermodel grannies".

Humans also make interleukin-11.³ Levels of it increase in the human body as we get older. The new process might have the same effect on us. Trials have already begun.

This is an enormous breakthrough. Extended youth is on the horizon. Maybe eternal youth will follow.

Humans are obsessed with holding back ageing. Legendary heroes quested for the Holy GrailSomething that is eagerly sought after. The real holy grail was the cup that Jesus used at the Last Supper, for which Christians searched fruitlessly for centuries. and the Fountain of YouthA mythical spring which is said to make those who bathe in or drink its water young again. . Today we cover our faces in creams made from crushed insects and snail slime.

Romans drank the blood of slain gladiators to gain their youthful strength and energy.⁴ In 2016, tech billionaire Peter Thiel made headlines when he said he wanted to inject young blood into his body.⁵

Philosopher Stephen Cave writes: "Our culture is based on our striving for immortality." People have built monuments, written poems and conquered nations in an attempt to leave an everlasting mark. Religions are built around the idea that we can live forever in the afterlife, without the infirmity of old age.

Imagine a life where we never start to slow down. Our joints and limbs never ache. Injuries would heal so quickly that you could play your favourite sport forever.

Think of the societal benefits too. Many countries now face an ageing population. With age comes illness. Hospitals are crammed with elderly people.⁶ Eternal youth would clear the waiting lists.

And what about youthful beauty? People spend billions of dollars to look and feel young. The richest morph their bodies with plastic surgery, sometimes facing grisly side effects. Eternal youth could bring everyone to the same level.

Yet some say that mortality pushes us towards greatness. If Carlos AlcarazVery successful Spanish tennis player. had his current fitness and flexibility forever, would he push himself so hard today?

Being young can be exhausting. As Ancient Chinese philosopher Confucius said: "Old age, believe me, is a good and pleasant thing. It is true you are gently shouldered off the stage, but then you are given such a comfortable front stall as a spectator."

In his novel A History of the World in 10 1/2 Chapters, Julian Barnes depicts an afterlife where people can feel young and do everything that they want. Eventually everyone gets bored - and pulls the plug on their own existence.

Of course neither Confucius nor Barnes enjoyed eternal youth. If they did, maybe they would think differently.

Would you want to be young forever?

Yes: Only a fool would say no. Imagine: an endless life at the peak of health. The world would be your oyster. You could try out hundreds of different lives, never rushing blindly down a single path.

No: Eternal youth is definitely better than eternal ageing. But it is still a curse in disguise. Maturing is one of life's most interesting experiences. And we would lose any sense of youth's specialness.

Or... Youth is overrated. The real prime of life comes later. If you had to live forever, surely you would want to be in your 30s or 40s: young enough to be dynamic, old enough to be respected.