I know all about mortality. I’ve known about this stuff for years. When I was young, I went out with a guy who was 20 years older than me, the age I am now. He discussed his health – I don’t know, sometimes a memory is a caricature, but I think it was all day long. It was like listening to Radio 4: the hard talk in the morning (cancer, MS, early-onset dementia); the speculative What If? mid-morning magazine show (“Maybe I’ve had herpes since 1979”); oddments and curiosities in the afternoon (“What is this mole? Are my wrists larger?”); surrealism late at night (“What does it mean when you get out of the shower and can’t remember whether or not you’ve washed your hair?”). When there was nothing wrong, he would reminisce.

This, for anyone who hasn’t tried being 43, is the reality of the second half of life. Things change. Senses diminish. And the brute fact is, something must be done.

I find self-care a hateful, icky phrase. I still have most of my identity invested in being the kind of person who eschews guidelines, scorns mindfulness and awareness, and eats vegetables only by accident, when they’re under sauce. But I have become, simultaneously, inconveniently, the person who wants to be a hardbody. I want to do things that make me live longer. Some elements of decline I can manage with denial (I don’t need glasses; I’m just no longer going to read small things) but my lust for life has its demands.

Don’t get me wrong: I do occasionally move my body. I’m a passionate cyclist, but at the moment all my passion goes on hating other road users while I cycle like a great-aunt who doesn’t want to be too early. I’m also a keen climber, but right now that means going once a fortnight to laugh at the instructor’s arms (seriously, they are as long as legs) and critique the can-do slogans (“The best climber in the world is… the one who’s having the most fun!”). But I want to go faster on my bike than a person with a beard. I want to be the first to own whatever’s the next spiraliser. I want it all: a carapace of insouciance over rock-hard triceps.

This is an abominable thing to want, vain in every sense. But I’m going to set out to do whatever it takes not to decay faster than other people, and report it accurately and fairly. Next week I’m going in a machine that tells you how old you are, really, at a cellular level. Even before you hear my health and fitness insights, you should be grateful to me for being honest about my ignominy.