For my 49th birthday treat, I went to see Shakespeare in Love at the Noël Coward theatre in London. Expensive but worth it: spry, funny, uplifting and moving but also, for all the surface froth, quite a deep meditation on the creative process and the enduring power of art.

What everyone secretly loves best about it, though, I suspect, is the way it so shamelessly flatters their intelligence. We’re all aware that Shakespeare wrote a sonnet that begins ‘Shall I compare thee to a summer’s day?’; that Marlowe was stabbed to death in a pub brawl; that Malvolio wears yellow stockings and cross garters. This is basic, middlebrow general knowledge. But the way the show plays with these details and weaves them into the plot without bashing you on the head or over-explaining has the pleasing effect of making you feel like you’re in on a private joke which only an exclusive few get.

The performances in the new stage version are a delight, especially David Oakes’s languid Kit Marlowe and Lucy Briggs-Owen’s adorable Viola De Lesseps. But the thing that really makes this production sing is the live incidental music (as was also the case with two of the other excellent productions I’ve loved recently: War Horse and the RSC Richard II). Nothing quite beats a nice bit of crumhorn or viol or plainsong or rustic balladry to get you in the right period mood.

Don’t worry, though. This isn’t an audition for Lloyd Evans’s job. I’d absolutely bloody hate to be a theatre critic, not least because I remember from my time as a showbiz correspondent in the early 1990s that perhaps eight in every ten productions you have to see are dross. Rather, I wanted to muse a little on the career choices I’ve made and on the regrets that now haunt me as a result. Fellow nearly-fiftysomethings — and post-fiftysomethings — will I’m sure understand where I’m coming from. Time is running out and the options are closing by the day.

For example: why couldn’t I have been a countertenor like the one in the show’s Elizabethan ensemble? All right, I can’t actually sing, so it was never a likely possibility. Even so, wouldn’t it have been a marvellous, esoteric and satisfying way of earning a living: playing obscure instruments — the hurdy-gurdy, say, or the impossible, long, valve-free Elizabethan trumpet — and singing like a dandy eunuch in churches and specialist theatre productions and beery folk festivals?

And presumably, if you’d done that then you probably wouldn’t have frittered away your youth. Rather, you’d have been something like an organ scholar at your Cambridge college and never have had time to take drugs or fruitlessly pursue meaningless sex, because you would have been far too busy practising your lute and your shawm and your wassailing. But the camaraderie and discipline of the ensemble would have more than made up for the absence of vice. Plus, you would have perfected skills which would have stayed with you forever, pulled nice birds and delighted you in your old age.

So there’s just one example of things I’m never ever going to do. But there are loads more: skateboarding; mountaineering; fencing; high-level tennis, golf or bridge; Chinese; Russian; Portuguese; running my own business; kitesurfing; becoming a master of foxhounds; flying a combat jet; going to war; swimming the Channel; sleeping with a supermodel; being in a rock band; taking silk; completing the Marathon des Sables; free fall parachuting.

‘Ah, you’re never too old,’ they say. But it’s not actually true, is it? For example, I know I’m still fit enough to do a marathon, but my knees are going and it wouldn’t be worth the damage. And yes, if I really put my mind to it I could still just about conceivably become an MFH. But where would I get the money, on my salary, to afford even one day’s hunting a year, let alone a whole season’s worth?

That’s the terrible thing about getting older. It’s not just the physical decline — the thinning hair which makes women below a certain age look straight through you; the knees and feet (any suggestions? I hate having to cut down on my running); the condor moments where you’ve gone upstairs to find something but can’t for the life of you remember what. It’s the closing down of career options, of doors generally.

When you’re in your twenties and thirties, you still have the luxury of being able to say to yourself: ‘Yeah, I’m sure I’ll have a period living abroad at some stage. Australia, maybe. Or the US. Or the Far East. Or Paris….’ But at touching 50 it’s not so easy. On the one side you’ve got aged parents, on the other, you’ve got children happily settled in schools.

Or even if you just stick with your home country, the options start to close. I love Northamptonshire, now, but the other day I had to drive to Fordingbridge in the New Forest and thought: ‘God it would be nice to live in Hampshire. All that forest to go hunting and mushrooming in, the sea, pleasant climate, nice people, still recognisably English…’. And I know now it just ain’t going to happen.

And that entrepreneur thing. Yes, I’m aware that there’s precedent for people starting businesses in their fifties or even in their sixties. But the consequences of failure are so much greater. There’s so much less time available to recover from your mistakes and give it another go.

Then there’s the curse of success. If you’ve been pursuing the same career till your fiftieth year, chances are you’ve got really proficient at what you do. The terrible thing is — and I mean this as no compliment to myself — I’ve become hideously well established as the king of right-wing snark because I’m just so damned good at it. But why, oh why, in God’s name, did my forte have to be journalism rather than hedge-fund management?