Turning 40 is a big moment in anyone's life and, for Chris McGuire, it is going to coincide with a few life changes

There are some things you never forget.

They just stay with you forever, like the phone number to call Going Live (ask your mum) or expert technique for eating a Twix, that leaves you with two pristine biscuits.

I'll never forget the moment when, as an eight or nine year old, I stumbled into the bathroom to find my dad dyeing his hair. The shock was huge. I couldn't believe his youthful jet-black mane wasn't natural!

Where am I going with this?

Good question.

I don't dye my hair. But I've just realised that I'm now older than my dad was at the point that I discovered he coloured his – in a vane (or should that be vain?) effort to halt the ageing process.

All of this makes me feel pretty old.

Basically I'm just about to turn 40, an age which I always considered to be the sole preserve of mature, life-sorted-out, 'proper' adults. I don't feel like a 'proper' adult – I, as you know, still remember the phone number for Going Live (Live and Kicking also used the same digits, but that's probably TMI).

Yes, my 40th birthday is looming like the sword of Damocles, just days away. They say, that as you get older, police officers look younger and younger. I've had a different phenomenon. People who I assume to be my age or older, keep turning out to be younger than me! Even Superman is younger than me!

How did that happen?

I think I've the age equivalent of 'imposter syndrome', it still surprises me when adults call me 'Sir'. In my head I'm still 21. Which means that The Big Four-oh is something of a surprise.

All of which means I'm going to have to start acting 'mature', like cheese. I'm going to need to talk about the weather, like I care. I'll have to start nodding enthusiastically when neighbours mention their hardy perennials and from now on I'm not allowed to miss a single episode of Countryfile – God help us.

Why? Well, as we all know, 'Life' is supposed to begin at 40. This mantra has been screaming out at us from greetings cards for decades. Personally, I think it is a pivotal age, but I'd like to swap 'begin' for 'changes'. I think 40 is the age where I need to start putting the ways of youth behind me. I do believe that, otherwise I worry I'll turn into one of those people who are stuck with the haircut, fashion and world view they had when they were 22. You know the type, their 1977 selves preserved in aspic, but for a wrinkle or two (dozen). Pretending that time hasn't moved on, doesn't do anyone any favours – except, that is for the plastic surgery industry who're making a fortune out of it.

Where was I?

Essentially my 40th is just about to occur and it's time I made some subtle changes – one or two at least. But please don't worry, these changes won't include giving up cake (I love birthday cake, if anyone's listening) or spending too much time in Lycra (on my bike, not mowing the lawn).

I do have one final thought, if you see my dad on your travels, don't tell him I've let his hair colour cat out of the bag – he'd dye with embarrassment.

Chris McGuire is a writer and stay at home dad. Check out Chris's new book, 'The Modern MAMIL: How to look pro', illustrated by Spencer Wilson, published by Ice House Books, a hilarious look at the cycling culture of middle-aged men in Lycra – out now