Kirsty McKenzie was living in a small Spanish village full of retirees in her late twenties when she was introduced by a mutual friend to Sue and Dave during a lonely Covid lockdown. The couple were in their eighties and had bought a second home in Estepona years before Kirsty arrived in 2020. "I went to dinner with them and after about three bottles of wine we had become fast friends," says McKenzie who, nearly 30 and single, had been missing her family and was scared she'd scuppered her chances of one of her own by moving abroad for work. The trio chatted about everything from politics to romance. "I really counted on them as surrogate grandparents. They calmed my anxieties about what it means to live a well-rounded life." They've stayed in contact ever since. "We all love to travel. Love to eat. So, we're often bonding over late nights in tapas bars. There's virtually no limit to how much white wine either of them can put back. It's always 'one for the road' and Dave repeats that until 3am."

Age-gap friendships are common. Nearly four in 10 adults have a close friend from a different generation, with more than half of Britons reporting a friendship with a 10-year age gap, according to YouGov. Although romantic age-gap relationships routinely prompt scandal and steal headlines (just look at Leonardo DiCaprio, Aaron Taylor-Johnson or Brad Pitt, each of whom is with either a significantly younger or older woman), platonic friendship across the generational divides is a surprisingly common part of ordinary people's lives, too.

McKenzie's particular meet-cute is unusual however: it's most typical for these relationships to blossom at work. "The office is a fertile place for people [to befriend those senior to them] because you're often forced to interact with somebody from a different group," says social psychologist Dr Libby Drury. "There's still so much ageism that is accepted within our society but the diverse friendships in the office often have benefits beyond the workplace. It can make you more open-minded and tolerant of other people."

Katie Jenkins met Angus when she was a 23-year-old trainee journalist and he was her 51-year-old editor. "I found him really intimidating," she says. "He was a gruff, no-nonsense Kiwi and the biggest grammar pedant I'd ever met. But he quickly became a brilliant mentor - and a good friend. He is genuinely (and perhaps surprisingly, given my first impression) one of the most caring, selfless people I've ever come across." All Jenkins has to do is lament something inconsequential like brittle nails, and Angus will appear with a cream that might help. "One time I was complaining about the enormous rose bush in our garden and he turned up with a pair of shears and helped me prune the damn thing," she says. "Friends my own age show love by buying cocktails; Angus shows it by trimming a garden hedge. I'm not friends with Angus because of his age, but I'm glad I wasn't deterred by it."

The UK is among Europe's worst countries when it comes to ageist attitudes, with new research from AgeUK finding a third of people over 65 have been discriminated against because of their age. Although half of us may have a friend who is a decade our senior, these relationships tend to become rarer as age increases, with the same number admitting they do not have a single friend over 70, according to the European Social Survey, which tracks societal shifts across the continent. The older you get, the more invisible, it seems, you become.

Yet there are many social, societal and health benefits of age-gap friendships, particularly for younger people. Those who build connections with people from a different generation are less likely to think that competence declines with age, says Dr Drury. "That's really important because if you internalise that kind of stereotype, it's actually damaging to your health. It's called stereotype embodiment theory." Essentially, if you believe all older people are doddery and frail, you're more likely to become that yourself in your later years. And the benefits work both ways. Older adults with friends more than 10 years younger feel happier as the years go by, which can lead to huge health advantages, including a longer life.

"The thing I get most out of my friendship with Katie - apart from the fact she's lovely company - is her vitality and passion," says Angus. "She's a wonderful conversationalist and storyteller - the opposite of me - so it's nice to hear about her life, family and tribulations. She's half my age, but she's my intellectual and emotional equal and I love that about her. She lost her dad as a teenager, so I guess I bring some fatherly advice to the party, but I'd like to think we enjoy each other's company because of a mutual respect. I certainly don't feel like a dad when I'm having a drink with her," he adds. "Katie is simply a lovely woman - and she still will be when she's my age. She's also very mature - arguably more so than me sometimes, and I consider myself lucky to call her a friend."

Since the beginning of time, there's been a generation war going on. Right now Boomers, Millennials and Gen Zs can't seem to agree on what socks to wear, what emojis to use, how often to go into the office, or who to vote for. A willingness to be open is the key criteria to build collective confidence for intergenerational companionship. "A lot of people have anxiety about interacting with somebody that's not from their social group due to intergenerational tensions," explains Dr Drury. "People aren't sure how they'll come across because they have no experience of the other group." Instead of interacting, we often enter a stand-off - or don't bother to speak at all.

What's more, let's not forget that Gen Z are lonely too. One in five people aged 18-24 have one or no close friends, a proportion that has tripled in the past decade. Research points to a "collapse in community" as the reason for this. While we happily interact with strangers online, Gen Z are more likely to distrust their neighbours and significantly less likely to think the people around them are trustworthy - let alone good candidates for friends. No wonder that, when a friendship is struck across the decades, it often feels so special.

Daisy Boulton was a first-year drama student when her favourite actor Harriet Walter, most recently known for her roles in Succession and Wolf Hall, miraculously appeared at the Diamond Jubilee street party her parents were hosting. She was too embarrassed to make contact herself, so her father bowled over to the Olivier award winner and informed her she was his daughter's favourite actor. Walter walked into the kitchen where Boulton was hiding and started chatting to her about the theatre. "We just got on immediately," Boulton says. "Then she came to see my first public show [Shakespeare's As You Like It]."

Boulton, now 35, still regularly goes on walks, for coffee or out to industry events with Walter, who turned 74 this September. "She's so smart and has such experience and wisdom, yet she always wants to know what you think," she enthuses. "Harriet reminds me to be curious as I get a little bit older. She's open in her intelligence, which is what makes her so smart."

For Chris, a 60-year-old writer who routinely mentors and socialises with people years his junior, the appeal of age-gap companionship is simple. "I have several younger friends, and for me, traditional ideas about youth and experience are irrelevant," he says. "I've watched bands with them, taken acid with them, stumbled out of taxis drunk with them. Most people are pretty much fully formed by the time they're in their twenties - and may be as brilliant as they're ever going to be. They're also hilarious in new ways, have exciting ideas, different mores, a different language and like different music. (I've seen those flares before, though).

"The comedian Dylan Moran once said, 'the great secret of having friends as you age is being able to 'suffer entertainingly' among peers who are similarly falling apart," he adds. "I think having a younger friend is the perfect antidote to that."

If your workplace doesn't offer the opportunity for intergenerational interaction, Drury suggests signing up for one of the many programmes in the UK designed to bring young and old people together. In 2023, LinkAges matched Cambridge PhD students in need of accommodation with elderly people in need of company as housemates. AgeUK runs "befriending services" which match volunteers to a new friend, who they can chat to on the phone or visit in person.

"I thought, I would like another friend to come and have a chat with me and have a cup of tea," reflects Rose, a participant in the programme who felt lonely as the lengthy winter nights drew in. The charity matched her with a younger woman called Sarah, for whom she felt an instant affinity. The pair now meet regularly. "It's the best thing I could have ever done."