Let's get one thing clear from the off. Fifty is not the new 40.

At 40, chances are you still have kids at home yet to take their GCSEs. Your life revolves around driving them to dance rehearsals, clarinet lessons or whatever other extra-curricular activity you've compelled your spawn reluctantly to embrace.

You don't have a life. You just have the gaps in their schedules, brief windows of opportunity to fill with the weekly shop, walking the dog, or not having sex with your spouse.

That's the reason why, previously, whenever the idea of reviving Cold Feet was floated, I found it easy to say "no". Cold Feet is about Adam, Pete, Jenny, David and Karen (but, sadly, no longer Rachel).

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I didn't want to write about their offspring. For two reasons. First, Outnumbered had been there, done that - and better than I could.

And second, having lived through those years, I knew they weren't that interesting. It's all about the children. You're not even the lead in your own life story, just a supporting character in theirs.

But by 50, that's all beginning to change. Presuming you've been blessed or burdened (delete as appropriate) with children, they're likely approaching the age where they've got one eye on the door.

Nirvana beckons them, an intoxicating cocktail of drink, drugs and casual sex. Crushing student debt, too, but that doesn't need to be paid off for years, and, since the young can't see further than the next episode of Hollyoaks (only the goldfish has a shorter attention span), that's not a timeframe they feel they need concern themselves with.

In terms of Cold Feet, the characters are now approaching the age of 50. Their kids are mostly still at school, but are of an age where they no longer demand all their parents' attention, or even welcome it. Adam, Pete et al now have the time, the luxury, to turn their attention back to themselves, to take stock of their lives and ask: "What next?"

The first Cold Feet was about characters on the cusp of change. And so is the new series. Except now, it's not about settling down. It's about realising you still have a good 25, 30 years to live and wondering how you're going to fill the time until you die.

Middle age is fascinating. When the last generation was staring 50 in the bloodshot eye, they were already old. My dad didn't change job after that age; my parents were living in the house they'd occupy until his death. Change was something they avoided.

Now, few people have the choice. There are no "jobs for life" any more. This lack of certainty can be a scary prospect. The future is a blank canvas and you the artist. It's your choice what you paint. It could be Van Gogh's Sunflowers. Or Munch's The Scream. It all depends what's on your palette. The young have all the colours of the rainbow. From what I've observed, the middle-aged tend to have 50 shades of grey. And I don't mean in the sexy way.

It's easy to let the advancing years get one down. Depression is common among the middle-aged. I've taken the Black Dog for a walk myself. I was fortunate; I was only briefly brought low.

Medical intervention and the support of my family (not necessarily in that order) helped me to a speedy recovery.

I didn't fall into the abyss so much as peer over the edge into its depths. But there were a few days when I couldn't leave the house or even stir myself from the sofa. I'm not ashamed to speak of this. And so I told my friends.

What surprised me was how many confessed to having been similarly afflicted. For a while, our conversations didn't revolve around sport or politics, but the relative merits of the anti-depressants we'd been prescribed.

Was it ever thus? I can't imagine our grandparents popped pills as blithely as we do. But then, they lived through the war. They really knew what it was like to suffer.

My parents' generation often had a scotch and soda on returning home from work. Looking back, I realise this wasn't a way to unwind so much as to numb the pain. But none of our forebears went in for soul-searching like we do.

It's the cross we have to bear - constantly to be asking ourselves are we happy? Are we happy enough? If you find yourself posing that question, you probably already know the answer.

By this stage, you might think I don't like being middle-aged. You'd be wrong. It is complex is all I'm saying. It's a minefield you have to tiptoe through, but while you do, take the time to stop and admire the wonderful flowers, for there are many.

Health! God willing, and so long as you remember to floss, you should still have your teeth. In this regard, 50 is the new 40.

Sure, you might play golf (though I don't - stupid bloody game), but there's no reason why you can't participate in real sports, too, pastimes that require some semblance of athleticism.

Football. Tennis. For me, it's running. Last year, I ran my first marathon. In four hours and six minutes. I was hoping to break four hours, but on the day, screwed up my water strategy and had to stop to pee. Twice. (Cursed middle age!) But the point stands: a marathon! In my 50s!

Music. I remember my parents listening to Sing Something Simple. Or, as I liked to call it, Sing Something Truly Moronic.

At the time, they were younger than I am now. But their musical taste sucked. Ours doesn't. We the middle-aged listen to the same artists as many of our kids. Adele. Coldplay. Kanye West. (OK, maybe not the latter.)

It's perfectly reasonable that we might want to go to Glastonbury Festival. The lines between the generations are beginning to blur. Blur! There was a good band.

I've a theory. Life is a bell curve. You're born on the baseline, then rise through childhood and youth to the pinnacle - adulthood -where you stay a while to admire the view, before beginning the decline towards old age and inevitable death.

Dotage is at the same height on the curve as infancy, because they're very similar - you spend much of the time asleep, can't feed yourself and have to wear a  nappy.

The optimum place on the curve is in your early 20s, when you're carefree, and not burdened by career, mortgage or fears your partner might be cheating.

But wait, look! There's an equivalent point on the other side of adulthood.

It's that period when the mortgage is manageable, the kids have gained their independence, and you have time and, hopefully, disposable income to burn.

It's your 50s and 60s. It's what used to be classed as old.

No longer! I think we should rebrand this stage of life. Not your second childhood. Children always have someone else they have to answer to.

No, let's call it your second adolescence, your olderlescence. I'm serious.

My wife and I are already planning ours. Next year our younger daughter intends to take a gap year. And we shall, too.

My wife's never been to India; I've never been to Japan. Before we met, we were both keen backpackers. So we shall dust off the rucksacks, update our Lonely Planets and take to the trail once more.

Except, this time, we won't have travellers cheques in our bum bags, but credit cards.
Roughing it is great, but it's even  better when you have the  option of an ensuite and complimentary bathrobes.