My trip to London last weekend included an overnight stay with old friends. Gill and I were at school together and flat-shared in London, until she and Martyn got married. I’m godmother to their middle child, Max, who’s now at university.

Having no siblings, I value these long-established friendships a great deal. When we get together, as well as catching up on the latest news, we inevitably end up reminiscing. Fifteen-year-old Alex was with us this time, so there was a need to fill in few details and answer her questions (hence the title of this piece).

That’s where it got scary. Because our shared experiences had to be nailed down, set into the context of our entire lives. It wasn’t enough to say those happy times were before Alex was born – of course they were. We had to admit it all took place thirty years ago.

Suddenly, telling yourself that 50 is the new 30 doesn’t work. And that’s not all. You find that gaps have appeared in your memory. Completely illogical ones. I remember the monthly rent Gill and I paid to share a room in a flat in Fulham with two guys from Bournemouth (£15 each). However, I can’t recall why the balding one, Phil, was always known as Blue. Perhaps reassuringly, neither can Gill.

Going further back, I can effortlessly call to mind the registration number (ARU983K), model (Vauxhall Viva Estate) and colour (sickly green) of the car my dad drove when I was 12. Perhaps I should make this the benchmark by which to measure any slippage into senility, and instruct my GP to make a note in my records to ask the appropriate question every few years?