As the father of a four-month-old and a two-year-old, I’m currently caught between two extremes. I have a child who needs carrying everywhere, feeding, dressing, changing, soothing, nurturing and supporting, and a child who is Miss Independent, insisting she walk everywhere, feed herself, dress herself, use the big toilet, and do whatever she wants, whenever she wants, without parental supervision. Unfortunately, I’m only talking about one child: my eldest daughter Izzie.

I’m constantly reminded of that Britney Spears song, ‘I’m not a girl, not yet a woman.’ For my daughter, it’s more like, ‘I’m not a baby, not yet a girl, because I don’t want to be either, except when I do.’ Which makes parenting her a bit of a nightmare at the moment.

One minute she’s refusing to wear a nappy because ‘me not a baby, daddy,’ bragging to her friends that ‘me wearing Peppa Pig pants!’ and using the toilet because she’s far too grown up for the potty; and the next, she’s screaming because she isn’t wearing a nappy, refuses to wear pants, and won’t go on anything because ‘me not a big girl!’

Four months ago she started to make representational art forms – a wooden brick airplane with wings and a tail – yet one day last week she assured me she didn’t know how to walk. She’s caught in that awful netherworld of identity between the easy, dependent life of an infant and the scarier, independent world of the little girl.

It’s obvious why – she sees her baby sister getting the attention and monopolizing our time and she wants the same for herself, but she also wants to play with her friends, do her own thing, and have some control over her life. Sure, it’d be nice to keep her a baby, but as she gets older it’s inevitable that she’ll have to leave that world behind.

Which her younger sister Rosie is doing right now. The first three months are sometimes called ‘The Fourth Trimester’ because you have a child that is little different from a baby in the womb, only you have to feed it and change it as it doubles in size and keeps you awake at night. But around three months she suddenly started to become interested in the world. She gurgles and snorts, smiles and laughs, and squawks like a cockatoo. Loudly. All blooming day.

And she’s become mobile. She rolls from her front to her back, from her back to her side, and, a couple of days ago, mastered reaching and grabbing hold of objects and steering them into her mouth – my necklace, my glasses, my beard. And that helpless little baby is now well on her way to a P60 and National Insurance payments.

It’s a confusing time. You want to tell them to slow it down, to accept who they are at this stage of their lives. You want to tell them to keep their fear of the dark because life is more exciting that way, and to hang onto their beliefs in a world bereft of magic. You want to tell them to stop wishing it all away.

But I remember being five years old in reception class at school, desperate to be older. I remember feeling powerless and small and longing to be autonomous and as big as the sky. I told the dinner lady, and she said that when I was older, I’d wish to be young again. I didn’t believe her. Who would want to be young? So I know my daughters won’t listen to a word I say, will only see the benefits of getting older and not what they’re leaving behind, even as we parents pine for the youth we lost.

But maybe they’re right after all. As a society, we glamorise youth and villify ageing – innocence and beauty and purity don’t have grey hair and wrinkles and saggy bottoms. We seem to spend our lives longing for some mythical time when we were happier and had it all in front of us. But why do we always define ageing by what we’ve lost instead of by what we’ve gained? Experience, stability, stature. A wealth of knowledge and the wisdom to wield it.

Instead of seeing ageing as decay, why don’t we see it through the eyes of our children, as a natural progression towards the people we want to be? Because each day we are becoming more, not less. Each day we are gaining, not losing. Ageing is not the enemy – it’s our perception of ageing, of what it means, that makes us suffer.

So whatever age you find yourself, embrace it. You are exactly the age you’re meant to be, and the features of that age are beautiful and yours to own – even hair loss and premature ejaculation. And that wonderful time long ago when we were happy to be young?

It never actually happened.