I’m going to be running the Windsor half marathon in 2 days, and I don’t want you to sponsor me.

People have all sorts of good reasons for running events. Me? Mostly I run because I enjoy it and it keeps me as chilled out as I ever get. I often forget how lucky I am to be able to just get up, go for a bit of a trot and then do whatever. Eventually I’ll probably be too old and broken to do this, but I’m rather hoping that’ll be because I wear myself out.

The thing that I feel luckiest for is that right now is that if I want to get up and run, I can (and I do). It’s a part of who I am. My enduring hope is that even when I am too physically broken to be active, I’ll still be alert enough to still enjoy life (and as we all know, Britain needs more lerts). The thing that scares me most of all is losing my marbles and not being me any more. I saw it happen to my grandmother - she had Alzheimers, and went from being her to not being her over a period of years, and her loss of control over her life was terrifying to her. And me too.

I’m resigned to the idea of eventual decrepitude - it’s what appears to happen in the absence of fountains of eternal youth. Given the evidence it turns out that I’m not 21 any more, and I’m mostly OK with this. The thought of losing all control, and my identity scares me silly.

I will be donating some money to the nice people at the Alzheimers Society, and for the sake of your marbles it would make me happy if you did too. Not because I’m going to go for a jog round Windsor Great Park, but because it’s the right thing to do.