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Sisters Cara, left, and Poppy Delevingne.

Strait-laced, anxious, ambitious, domineering. Have you ever been called any of these? If you’re an older sister, like me, I’m willing to bet you have. When it comes to family hierarchy, we all have our set roles. And traditionally, the big sister is seen as the high-achiever; the sensible one. Our lot is to blaze a trail. We pave the way for our little sisters’ easy and carefree passage through life. We’re the first to reach every milestone: the first day at school, the first to sit exams, the first to fail a driving test, the first to bring back a member of the opposite sex and to fly the nest.

The little sister? By contrast she’s a free spirit — and can usually get away with murder. Which is why I felt a pang of empathy for Amal Clooney this week. The human rights barrister and her actor husband George were joined by their families at a restaurant near the Clooneys’ holiday home on Lake Como.

Amal appeared at dinner chic and sophisticated. But, for once, she didn’t grab the headlines. Why? Because of her little sister, of course. Tala Alamuddin is an events planner who lives in Singapore with 12-year-old daughter Mia, from her marriage to businessman Nagi Jamiyeh. She arrived with a beaming smile, wearing what can only be described as a bright red jumpsuit, which she’d caught in a revolving door and ripped one leg clean off.

It was edgy, glamorous and fearless. And it perfectly encapsulated the relationship between older and younger sisters. Amal appeared controlled and elegant. Tala? She looked like the sort of woman who could stage an Ocean’s Eleven-style casino heist and then splash the cash on diamonds and outrageous one-legged couture.

It’s a pattern we’ve seen again and again with sisters in the public eye. The older comes across as level-headed, the younger seems to have all the fun. Think Poppy and Cara Delevingne, Kylie and Dannii Minogue; Savannah and Sienna Miller; Kate and Pippa Middleton. Of course, the Middleton comparison is tempting. Both Tala and Pippa were thrust into the public eye at the wedding of an older sister to a high-profile man (Amal and Clooney married in Venice, last September). And both wouldn’t have remained there unless it was for their sibling’s love match.

But while Amal, 37, and Tala (age unknown) — not to mention Kate and Pippa — might look uncannily alike, don’t be deceived. These sisters are as different as any others; trapped in the sibling merry-go-round. I have two younger sisters, who happen to be twins. Growing up, I was aware from an early age of the responsibility that brings. There are four years between us, which now counts for nothing but at times seemed like a gulf.

When I started secondary school, they were still swapping stickers in the playground. When I went on my first date, they weren’t in their teens. As such, the older sister is expected to act as an example. It can be a little overwhelming. Mum and Dad don’t mean it, of course. They’re hard-wired to push you to greater heights. It’s no coincidence that users of the online parenting forum Mumsnet refer to eldest children as PFBs — Precious First Borns.

Just look at Kate Middleton, the Duchess of Cambridge — herself an older sister and reportedly the product of a “pushy” mother. Carole Middleton, we’re told, played a significant part in propelling her eldest daughter out of middle-class anonymity. Little wonder, then, with all that pressure, we older sisters can look like the weight of the world is on our shoulders, while younger ones can get away with being carefree sprites.

It’s also why we’re astounded when younger sisters claim to have been at a disadvantage. The assumption is that, as the eldest, you’ve been born into privilege. Like all that attention was a good thing. Well, given the chance I’d gladly change places with any younger sister. By the time my sisters were in their teens, no one minded much which GCSEs they took or how late they stayed out at the weekend. Me? I was practically thrown to the lions for not appearing at the door before 11pm. My mother, when pressed, admitted that, by then, she just gave in to my sisters for some peace.

And that’s the rub. We’re rarely happy with our performance. Studies have found that older siblings have a higher risk of depression, anxiety and heart disease. In 2012, the scientific journal Economics and Human Biology reported that having a younger sister (or brother) can raise your blood pressure by 5 per cent. I assume that’s per sibling. But while we older sisters beaver away, our little sisters are busy turning the art of pulling silly faces into modelling careers (Cara D) and hitting the London party scene (Pippa M).

It’s little sisters who pierce their belly buttons, get tattoos in Thailand and shrug at less-than-perfect exam grades. They rock up to a family party wearing asymmetric onesies, while we opt for something “suitable”.

But what no older sister dare admit is that they quite like being seen this way. Because, beneath the sensible, dutiful exterior lies a naughty side. While a younger sibling’s behaviour becomes part of their personality, an older sister can hide her wilder tendencies beneath a veneer of prudence and a knowing smile. So really, deep down, I suspect Amal is every bit as fun as her younger sister. And she’s probably got her belly button pierced to boot.

— The Telegraph Group Limited, London 2015