At the book festival in Edinburgh last week, a reader of this column - I do have some (1) - came up and told me, very kindly, that I look slimmer in real life than I do in the picture below.

Obviously this made my day. My lighter-than-it-would-appear self floated through the rest of that afternoon and well into the night. Until I caught my stomach on the car door.

Of course I'd like you to believe I don't really resemble this picture. It's been Photoshopped extensively, I tell everyone. "I've asked the picture desk to add 15lbs, maybe even 20, to disguise my naturally whippet-like physique," I'll say. "Really, you can't trust any picture byline you see in this newspaper. You don't think Fidelma on the inside back page actually looks like that? I've heard she's really a twentysomething black girl from Dunoon who doesn't even like dogs. Frankly, I wouldn't be surprised if the nearest she's been to France is buying a skinny latte in Pret a Manger." (2)

Obviously I can only get away with this when talking on the phone. I do like the idea of being able to Photoshop your life, though. Take a few lines off, massage the curve out of a pot belly, tighten up the jawline, and all without the requirement of cosmetic surgery. If only. But, as the very fine Israeli cartoonist Rutu Modan said during one session I attended in Charlotte Square, the problem with life is, it's too bloody linear. It keeps going forward relentlessly, day after day. It never doubles back or circles around. And so you're left mourning the memory of what once was. Rutu said she's got a 11-year-old son whom she loves dearly, but now and again, she said, she wishes he was still a six-month-old baby.

Last week I brought daughter number one into Glasgow for her first day at college. She walked off into class, this tiny slip of a girl, and as she did I felt my heart crack like an egg dropped on a stone floor. How can she be 17? I don't want her to be a grown-up. She's still my child. The one who was only just running around in the back garden, falling asleep in her baby seat in the back of the car, making her arrival into the world at 10.10pm one night in June. (3)

That's nearly two decades ago now. But in my head she's a baby, a toddler, a schoolgirl, a sulky teenager; all these iterations of the same person, all co-existing, all alive to me still.

But then in my head I'm slimmer than I appear in my picture. I guess only one of these things is possible. And I'm not even sure about that.