“YOU’RE only as old as you feel” goes the saying.

Well, I feel really old – and here’s a significant birthday to prove it. By the time you read this, I will have passed beyond the threshold. In an instant, I’ll have gone from under, to over, 50.

I know that’s hard to believe from my youthful good looks, but that photo of me at the top was actually taken just after they invented cameras. I look more like a badly crumpled Father Christmas on Boxing Day now.

Turning fifty is remarkably similar to your hamster dying. You feel sad, lost, bereft and angry. “Why?” you yell, while waving your fist impotently at the sky. “Why has Hammy McHamsterface gone?! I should have paid him more attention! We should have had more fun! All those years – wasted!”

Like mourning Hammy (RIP), it isn’t something that your friends and family can help with much. They don’t share your sense of loss and bewilderment. They won’t tell you that you’re over-reacting to your face, but you know they’re thinking it. They just can’t understand that it isn’t only about unfulfilled hamster-related dreams – it goes so much deeper than that.

It hits you suddenly too. Just days before, I had my first taste of what it would be like. Discussing the no-longer-legal-tender £5 note, I mentioned to my younger friend that I still had a £1 note at home. After a confused silence, she said “There was a £1 note? When did they introduce the £1 coin, then?”. “1983”, I replied. “I wasn’t born then...” came the response. Wow.

Any day now I could be working with someone who was born this century. How did that happen? The last 30 years since I was a teenager have flashed by. It seems like yesterday that I was using styling mousse in my luxuriant hair, and popping on my espadrilles and thin leather tie (the one with piano keys on it) for a night out. Now I’m contemplating elasticated waists on trousers, wondering if anyone will notice if I slip off to bed before 10 and peering over the top of my glasses a lot with a puzzled expression on my face.

Even converting my age using a KPH to MPH formula doesn’t help. I can’t remember much about being 31 anyway – I’ve successfully blanked most of the 1990s out of my ageing mind for crimes against music, and the fact that I wasn’t in my 20s any more.

Still, there are good things about reaching half a century, right? Please say yes. I can’t think of any. So, as I sit here writing this, I’m staring down the barrel of being an over-50. The toddler-me in his Batman shirt had no inkling this was coming. I envy him - although he didn’t have any Star Trek socks.

Actually, there’s a positive. I’ve been reduced to smugly trying to get one over on my two-year-old self. Goodbye, cruel world. See you on the other side...