Harriet Walker: 'Pretending to be a grown-up is the most clanging way of telling whether someone is still a child'

It's ten years this autumn since I went to university. I'm aware that the natural response to that utterance is to say (usually triumphantly, with all the grim vigour of someone who has just slain a dragon), "Just wait until it's 10 years since you left!" or "Well, it's 30 years since I went!" or even "I can't remember university – was it like when I had my hip replacement?"

No, I'm well aware that going to university 10 years ago marks me out as the sort of spring chicken that is only slightly tough when roasted. So don't worry, I'm not panicking about being old. (I seem to write that in every column now, which is invariably proof that I am, in fact, terrified about it. But I don't feel like I am, so bear with me.)

No, I'm glad to state that, after 10 years, there are a number of things I'm glad to have realised, or survived at least. A crowd of freshers got on my bus the other week, and I considered them as children, undeveloped and obvious, with their every mental calculation seemingly totally translucent underneath their skulls and their physicality as jerky and unlearnt as a toddler's.

Then I saw some other freshers on the news, talking about Syria as if they had a world view. As if the considered weight of all of their less-than-two-decades-on-the-planet were a real bargaining chip that made them worthy of being listened to.

Anyway, it's 10 years since I put on a lilac T-shirt, paired it with some lilac bootcut cords and thought I was not only ready to face the wider world (which, after Sheffield, is pretty vast) but to encounter class and prejudice for the first time, and have real experiences. I remember stuffing tissues into my armpits in the car on the way there, in case I sweated and people thought I was weak.

I had a mental list of things to do at university. They were, in very particular order, to fool everyone into thinking I was a grown-up; to learn to smoke; and to lose my virginity. I'm aware that the second two fuel the first only in so much as being desperate to do both is fairly indicative of a person who clearly hasn't grown up yet.

If I'd done it properly, I would have realised that pretending to be a grown-up is the most clanging way of telling whether someone is still a child. I would have realised that to be truly grown-up and worldly is just to ignore members of the opposite sex until you have something worthwhile to say to them (I think this kicks in at 40 once you've had their child), and smoking is just an extension of breast-feeding, because it gives you both a reason to leave situations you're not comfortable in and something to do with your hands.

If I'd done it properly, I would have realised that all the people who seemed so much more grown-up than me at the time were every bit as useless and juvenile as I was. That when they said they'd built a school in Mozambique, they meant they'd paid through the nose to have someone let them paint a single square foot of wall and pose for pictures with children more mature than they would ever be. That all their knowledge of how to use a gas hob was every bit as stylised as the façade I too was presenting to the world.

If I could be a fresher again, I'd go back and pretend to be as young as possible. To revel in my greenness. To say to myself, "Ten years on, you still don't know how to use a gas hob, or how to smoke, and losing your virginity… well, it's more hassle than it's worth."

Because if you're a fresher who shuns the weight of the world or the incipient realm of the grown-up – which, let's not forget, thanks to eternal youth, extended pre-middle age and creeping house prices is now put off until you're basically semi-retired – you're cool. You're open to new things, you're still fascinated by learning, and you're less likely to be the earnest one chuntering at a party.

My baby nieces started school this autumn, and they remind me of the best kind of freshers. Because they have no idea what they're getting themselves into, they can enjoy it all for what it is. Storytime is all the lectures I didn't go to because I was too self-conscious. The sandpit is all the occasions I didn't just go and have a good time, because I was waiting for someone to ask me. Realising your parents have left and howling – well, that's just as hard whether you're four or 18.

It's 10 years since I went to university and I might have learnt some things. But the main one is that to learn things properly, sometimes you have to un-learn a bunch of stuff first.