When my father was in his terminal year, I discussed death with him. I recall very clearly his relief that the cancer that was taking him was at least allowing him "all his marbles". Dementia in its varied forms is not like cancer. Dad saw the cancer in his pancreas as an invader. But Alzheimer's is me, unwinding, losing trust in myself, a butt of my own jokes and on bad days capable of playing hunt the slipper by myself and losing. You can't battle it, you can't be a plucky "survivor". It steals you from yourself. And I'm 60; that's supposed to be the new 40.

I saw them recently on their morning walk, and they caused me a pang. I have always wanted a pug and now I can't have one, because buying a puppy when you are too old to take it for walks is unfair. There are dog-walkers, of course; but the best part of owning a dog is walking with it, enjoying its delight when it detects the signs that a walk is imminent, and its glee when its lead is unsnapped and it can bound off over the grass, casting cheerful looks back at you from time to time to make sure that you are still in touch.

I’ve been very fortunate in that respect. In the early days I liked to be the bomb of the expedition, and rush on ahead and do things faster than anybody else. Those days merged very pleasantly into periods when I organized and inspired expeditions and selected these younger people who were then the bombs of the operation. And then it drifted into this involvement with the people of the area, still loving the mountains, but finding the people just as important too. And on and on it’s gone. As I get older and less physically capable, I find other challenges have grown up and become just as important to me.

I’m actually looking forward to getting older.

To a resistant materials teacher at secondary school called Mr Noel. He had a comb-over and whenever he turned his back to write on the blackboard, we would roll up bits of paper and launch them at his head. Once, I hit him. I remember him turning around and looking crestfallen.

Curious, playful and silly.

Finding a tenner in your jeans pocket. It has always been there but you find it at the moment you really need it.

When I was naive to the complexities of life.

Telesales – having to sell terrible kitchens. I thought, maybe I’m not a good actor because I can’t even convince myself that these kitchens are worth paying for.

Helen Mirren was in the elevator with me at the National Theatre. She pressed the button but it didn’t move. I said, “Fancy seeing you here and being stuck in an elevator.” And she said, “Was that meant to be funny?” I apologised, and she laughed. Even talking about it now, it feels so awkward and embarrassing.