"We have the results of your biopsy, Mr Simpson, and it shows the polyps in your colon were malignant."

The doctor who is telling me this is impossibly young, and pretty beyond any criticism. How old is she? She looks to be twenty, but that is impossible, unless she is some Hollywood version of Doogie Howser. Is it a sign of growing old when doctors look too young? What is the youngest a doctor can be? She cannot possibly be beyond her mid twenties. She is literally half my age, and there she sits, in complete control of my life, consummately professional.

"We've caught it nice and early. You're lucky," she says, and smiles encouragingly at me, as if to say, 'Congratulations, you have already passed through the first three stages of our competition.' I try and feel lucky. If I'm lucky she won't say what I know is coming next. Oh God in heaven, don't let her say it. Sweet Jesus, make it not so. Mary, Mother of God, strike her dumb.

She says it.

"We need to remove a section of your colon."

The world falls into soft focus. All I can see through tunnel vision are her lips, small, neat, scarlet, moving.

A colostomy! She could have said anything else. She could have said it was harmless. She could have said it could be cured with a dose of radiation. She could even have said it was incurable and I had only six months to live. At least then I would have a normal, albeit brief, existence. But not this, Dear God, not this.

She is talking, unaware that I have died and plunged into the deepest pit of hell. I hold my hand up, index finger raised, to stop those perfect lips from moving. She stops. I drag my eyes from her mouth, and she is looking at me with a mixture of concern and puzzlement. Between her beautifully made-up face and my decrepit old one stands my finger. It is shaking. I stare at it for a moment, unable to make the connection between what I am seeing and my own body. I hold my index finger to my lips in the universal signal for quiet, as much to stop it shaking as to silence her.

"I ..." My voice is hoarse, and shakes as much as my finger. I clear my throat and try again. "I'm sorry, I zoned out for a moment there."

And I am sorry, too. Sorry that I have been so rude as to not listen to her. Sorry she has to be in her position, to tell some stranger his life is ruined. And sorry, so sorry, so bloody sorry that I had to hear her tell me.

"You're going to remove a section of colon. Okay. Sorry, what did you say then?"

"Are you alright, Mr Simpson? Would you like a glass of water?"

Because that's exactly what I want; to pour liquid into my diseased and cancerous gut. I shake my head.

"It's okay, Mr Simpson. The procedure is so routine nowadays. There is minimal risk, and every chance afterwards that you will live a normal, active life."

I stare at her, willing her to hear the nonsense she has just said. She looks nervous, licking her glossed lips.

"I don't care about the risk. I'm not bothered about the risk. I don't care whether I die on the operating table or not. That's not what is bothering me." I sound as though I'm explaining why Daddy has to go to work to a petulant four-year-old.

She is perplexed, shaking her head. "What is it then?"

And suddenly I realise what her problem is. I see it as though I am sitting in the cinema, and the pastel walls of the consulting room are projected onto a huge screen. I see myself as she must see me: an old man, not yet geriatric, but too old to be anything other than just an old man. I'm over the hill before I've ever reached the peak. The audience compare the old, sick man to the young doctor, at the peak of her physical prowess, prettier than anyone she knows, a glittering career before her. What in this world could possibly be denied to her?

She looks at the characterless shell of a body slumped in the chair before her, and of course all she can see is his fear of death galloping towards him on time's winged horse.

"You wouldn't understand," I say, wallowing in the loneliness of the moment. At this second, at this exact point in time, no-one has ever been so alone. Even hermit monks that spend all their life in a cave have their God to talk to.

"Try me," she says, and behind her professional mask the set of her eyes shoots bullets at me for implying she's too young, too much of a girl, to do her job properly.

I try. "I'm fifty. I know I am, and my body is wearing out, and if I'm average I've got another twenty years, maybe twenty five, left in me. But not here, I'm not." I tap my chest with my fist. "Here, I'm your age. In here, I'm young and witty and clever and absolutely ... pigging ... gorgeous." I accentuate the last words, with all the conviction she must feel when she steps from the shower and sees herself in the mirror.

"I've been married nearly thirty years. Shit, that's longer than you've been alive. The day you were born, we already knew that we were going to be in love forever and ever, amen. She's everything to me, she is so much more than I ever deserved. Even now, when we're both past our prime, I look at her and just cannot believe that, after all this time, I can still make her laugh. We can sit out in the garden in the summer and talk for two hours straight. You'd think, after thirty years, we'd already said everything, wouldn't you?

"That's it," I say, gradually realising it myself. "That's what keeps me twenty. It's the twenty-year-old in her. She loves me, knowing everything I am. She can say anything to me, because we're best friends, and will be even after she's said it. She giggles like a girl when I flirt with her. And sometimes, when the moment is right, I'll just stroke her arm, and her knickers will go moist with lust, because she can see the twenty-year-old in me."

I'm choking with emotion, but the words are like a waterfall, a force of nature. The dam has broken, and nothing will stop them coming out.

"And I know her. I know her as well as she knows me. What's she going to feel? What would you feel? Would it turn you on? Would it?" The doctor is looking nervous now, and I know I'm sounding out of control. I am out of control, the words and emotions have a life of their own beyond my control.

"Could you feel sexy and turned on and full of lust with a bag of shit bouncing between the two of you?"

She looks embarrassed, like only the young can when confronted by an old person. She is embarrassed because of the unchecked emotion coming from a man too much her senior. She is embarrassed because she, the all-powerful doctor, doesn't know what to say to make it better. She is embarrassed by my use of the word 'shit'. But most of all, she is embarrassed by the thought of two old people having sex.

"People cope, Mr Simpson."

"Cope? Cope? Life isn't for coping. Do you cope, a gorgeous, intelligent young woman like you?" I throw young in her face as though it's an obscenity. "I don't want to cope, I want to live. I want to be like I was yesterday."

"You're wife loves you, I'm sure, Mr Simpson. You'll work things out."

I try to calm down. I realise that my voice has been rising. And then the anger subsides, it drains out of me as though the colostomy has already taken place and I'm unable to stop it running out the hole in my stomach. All that's left is self-pity and self-loathing.

"Yes, you're right. I'll tell her, and she'll be so sympathetic and understanding. And when it heals she'll put her arm around me and tell me she still fancies me and then we'll have a sympathy fuck, because she'll pity me."

The doctor winces slightly. For someone who peers up diseased rectums for a living, she has a curious sensibility to swearing. But for once in my life I don't care. This is the one time in my life I can be one hundred percent selfish. Wasn't it me that's just been told his life has ended?

"What can we do, Mr Simpson? You must have the operation, or you'll die."

She's right, of course. For all my protestations that I'd prefer to be dead, now that I have a choice I'll choose to live. For all I am mourning the death of my marriage as it was, I'll take the pity sex. Though I kid myself I'm a young man, I'll spend the rest of my years strapped to a bag of my own excrement, the young man forever dead, the old man forever reminded of his decrepitude.

And finally the tears come. I hang my head and howl, helpless and ashamed and unable to stop.

"There, there," says the doctor, quietly.

The theatre-goers see the scene in wide screen, the broken old man on one side, the pretty young girl on the other. We all know that what she should do is put her arm around his shoulder, but the gap is wider than the cinema screen. They are further apart than any two people have ever been, and she can't reach across.

"There, there," she croons, helpless.