I went climbing with a millennial. It was like a perfect political metaphor: she is younger, fitter, braver and more energetic. I am incredibly good at getting discouraged, having a rest and giving advice from the sidelines. She will cling on to a wall like a marmoset trying to escape certain death, whereas I will get near the top, realise how high that is and lose my nerve. Together we could make a formidable team, me at the bottom of the wall, going, “That’s great, try swapping your feet. Oh… What did you do that for?” And her going, “Shall we try that again so we’ve actually done it? Do you think we should have warmed up first?”

Climbing muscles, being the same as regular muscles, are use-it-or-lose-it. I climbed more often before I embarked on the lunatic running caper, and used to think of the green runs at my local centre as being for children, or for a warm-up. Now I find them devilish hard, and the purple is my top-of-the-tree, when in fact they are both for novices, really. I suspect the millennial of avoiding the blue-with-red-spots just so as to not show me up.

It wasn’t her first time climbing, but she wasn’t registered at the centre, so she had to go through a process that sounds intimidating: watching a video, answering questions on it (the answers are always “I am responsible for my own safety in the bouldering centre” and “Holds may spin”) and putting in her next-of-kin. In an older person – me, for instance – any activity that starts with a rumination on your own death is a little low-energy, whereas she seemed quite thrilled by it.

We both scorned each other’s clothing: she accused me of having the least appropriate underwear ever because apparently it poked out of the top of my leggings, while she was dressed to be a labourer-extra in a Levellers video circa 1992. The only thing that took the heat out of this was a guy wearing yellow shorts of purest parachute silk. The moral is that you can basically wear anything while you climb. It’s not like running, where the ill-dressed are chased from the area by a thousand eyes.

Everyone worries about their arm strength in climbing: you think about a person hanging off a rock and you assume, “They must have arms like legs.” In fact, only legs count. The millennial, I don’t think she’d mind my saying, has arms like twigs, yet could sprint up a wall as if she’d left her phone at the top of it.

And even legs are of secondary importance to brains. Neither of us had the patience to read a run before we tried it, so getting it repeatedly wrong was the only course left. When there are two of you, however, you only use half the energy per unit of knowledge. This is the best argument for going with a friend; the worst argument is that you spend a lot of time chatting. She was a much more dynamic climber than me, being bolder, but also fell off more often. I finished fewer runs, tried less hard, was less tired at the end. It was like an exercise buddy movie. I’d do it again, or help her fight crime, whichever she’d rather.

What I learned

If in doubt about your balance, clench your abs, then see how you feel.

• To find a club near you, go to ukclimbing.com. Zoe wears clothes by mygymwardrobe.com