OLDER people shouldn’t really blame younger ones for the gaps in their knowledge.

I often do, but I shouldn’t. They’re not necessarily to know that Hitler didn’t lead Germany in the First World War, and that the Battle of Hastings wasn’t a key campaign in that conflict.

If they guess that Henry IX succeeded Henry VIII, that the official language of Brazil is Brazilian, or that the Black Prince’s father was Old King Cole, then we should remind ourselves that they haven’t been taught otherwise yet.

Given the current closure of schools, it could be a long time before they are.

It’s when they miss cultural references that I find it most surprising. Maybe it’s only natural that these days they think of Homer as Bart and Lisa Simpson’s dad, rather than the author The Iliad and The Odyssey.

But when my 12-year-old niece scolded me for eating Mars bars, I told her: “But a Mars a day helps you work, rest and play,” and read a blank look on her face. Only then did it occur to me that that advertising slogan was last used before she was born.

So times and adverts change. But how could any of the young possibly be unaware of knock-knock jokes?

The puns with their formulaic scripts are said to date back to Shakespeare’s era.

They certainly date back to my primary school era. We used to hear them and tell them all the time. I don’t remember anyone falling off their chair with laughter at them ­— at least not by the time they were about eight or nine ­— and when I look back, there’s only one that raises a smile for me. I’m sure everyone of a certain age knows it.

Knock knock.

Who’s there?

Little old lady.

Little old lady who?

I didn’t know you could yodel.

I never got it until I’d seen The Sound Of Music.

According to researchers from Perspectus Global, one in five people under 30 have never heard a knock-knock joke. And three-quarters of all people, of whatever age, regard them as old fashioned and therefore no longer funny.

Maybe they never were really. But the idea that something isn’t funny because it’s old fashioned is very wide of the mark. Just because a joke or comic scenario isn’t new doesn’t mean it isn’t funny.

There are plenty of episodes in Shakespeare’s Twelfth Night that will raise a smile or an out-loud laugh.

The 17th century French playwright Molière is also full of enjoyable parts, especially his play The Miser ­— which should, of course, always be referred to as “L’Avare”, to suggest that you read it in French.

And yet Shakespeare and Molière were ripping off another, earlier comic playwright ­— the Roman writer Plautus.

There are puns that of course don’t work translated into English, but plenty of comic characters, situations, ironic comments and misunderstanding that elicit a laugh today, 2,200 years on. There’s a real fascination in realising that people 22 centuries ago were laughing at the same things we are laughing at today.

What it also shows is that a lot of comedy is quite formulaic and revolves around old personalities or situations retold in new ways.

Plautus has his dim-witted characters who are there to be laughed at. Then consider Manuel in Fawlty Towers, Baldrick in Blackadder, Trigger in Only Fools and Horses, Alice in The Vicar of Dibley, Joey in Friends and Father Dougal in Father Ted, to see that type being recycled.

I imagine anybody who set out to write a sitcom these days would feel the need to include a stupid character to be the butt of jokes.

And it doesn’t matter if such characters are familiar. As the great Frank Carson always said, it’s the way you tell ’em.

One surefire way to kill off a joke is to dissect it and analyse it as if it’s a specimen in a lab.

But many doctors take jokes quite seriously. They point out that laughter strengthens your immune system, boosts your mood, alleviates pain, and protects you from the effects of stress. Nothing works faster or more dependably. In other words, laughter is the best medicine.

I’m not sure I entirely buy that. These anti-Covid vaccines are pretty good medicines, too. You can’t just laugh off a pandemic.

But a good laugh certainly does no harm, whether you get them from knock-knock jokes, Private Eye or a DVD of Fawlty Towers.

Or try Plautus. They’re right when they say that the old ones are the best.