She's not very tidy. Just look at the state of her basement flat in Hampstead, best part. More like a squat. She herself is squatting, on the floor in front of her Apple Mac laptop, price pounds 4,000. There is no furniture, not even a sofa or chair. The floor is totally covered - dirty clothes, books, CDs, records, mugs, dishes, half-empty bottles, messages, notes, tickets, photos and dead ashtrays, full to the brim.
Somewhere, amid all this debris, are three large cheques. She remembers them coming, she remembers opening the envelopes, but now she can't find them. Her boyfriend, Taylor, is searching for them. They have run out of cash, even though these days Caitlin is earning around pounds 50,000 a year.
Not as plump as she looks on television, and much nicer, much funnier. She has a rare gift for words in one so young. On TV, they have her introducing or interviewing musical groups. They are her passion in life.
The fame she finds a drag. 'I never wanted to be famous. It was amusing at first, but now I hate it. I just wanted to be respected by people I respect. And I wanted to be rich. It's best to get rich, then you can do what you want.'
She comes from Wolverhampton, eldest of eight children, brought up in a three-bedroom council house. Her father is a musician, Irish-Liverpudlian extraction, who did session work with many well-known bands in the Sixties. Her mother went to Sussex University and has a middle-class background, hence Caitlin's rather proper tones, though she is fond of saying she is just a fat tart from the Midlands. Catholic-sounding father, hence all the kids? 'No, I was brought up Zen Buddhist.'
She was christened Catherine but later changed it to Caitlin. 'I have two stories. One is that I was studying numerology at the time, which gives numbers for letters and you work out how lucky you are going to be in life by the numbers, and I found Caitlin is luckier than Catherine. The other is that I was reading Jilly Cooper's Riders. She has a pretty girl called Caitlin who gets all the boys with names like Hugo and Archie.'
At 11, she did three weeks at Wolverhampton High School for Girls, but hated it, and asked to be taken away. 'They told you what colour knickers to wear. If I'd stayed at school I'd be a drug addict by now, taking heroin to stop me worrying about my knickers. Or I'd be working in a shop. Or perhaps I'd be pregnant. That would be nice. My mother has encouraged me to think of being pregnant since I was 13. I want lots, at least as many as her. You might have four kids you hate, but the chances are the other four will be your best friends.'
Caitlin was then taught at home, by her parents, as were her other brothers and sisters. 'We got inspected, now and again, and the inspector would give us biscuits. My parents didn't really give me lessons. Once I could read and write, that was it. I lived in the public library. I loved Ballet Shoes, brilliant. E Nesbitt,Spike Milligan and Harpo Marx's autobiography, though it wasn't very well-written. I have a vastly specialised knowledge. Ask me anything about satanism. I know how to bleed-ice a cake, but I'm shite at mathematics.
'No, I don't regret not going to college. Students learn up to the age of 21, then stop. I'll always be learning - the things that really matter in life. How to sign on, how to get free food, how to be streetwise. At my age now, I suppose I'd be first-year college, in the ordinary way of things, getting marks out of 10 for my thousand-word essay. Instead I get pounds 500 for every thousand-word newspaper essay. Which would you choose?'
She is about 10 years ahead of her contemporaries. But it's talent that's done it, not just her youth. She doesn't write yoof stuff. 'People think I'm a teenager, but I'm not. I'm a very old and weary woman.' Her style is polished, even poetic, so you couldn't really tell her age, except from her preoccupation with pop. Where did the style come from?
'I think it was having to appeal to all ages, all types, right from the beginning. I wrote my first book at eight, all of four pages. At 10, I did a 40-page story. At 12 I wrote two stage plays. One was called Are You Being Ignored and was set in a supermarket. The other was called Hello Bathsheba about a bloke who breaks his leg playing golf, decides his life is finished and becomes a Buddhist monk. I wrote everything to amuse my younger brothers and sisters - and my parents. I was trying to amuse all of them, at the same time. That's why I can now Entertain the Masses.'
She is also pretty organised in her work, if not her lifestyle. 'I was doing this column for the Observer at one time, and one week they didn't use it. It was really brilliant, all about how awful London is. 'Rats danced a Morse code of panic on the Tube line . . .'
'After four weeks of it not being used, I thought hell, I'll ring the Times, see if they'll take my stuff instead, and they did.'
She says she can always write, whatever her state. 'I can get home at four in the morning, unable to get out of the taxi, then I sit down and write my column. Having this new machine is brilliant. It's more fun than sex. I turn on the screen and can mainline the words straight into the computer. My brain is permanently overloaded. It dribbles out of my ears and leaves stains on the pillow.'
She has no agent at present, having sacked two. She likes to do her own deals, keep sweet her own contacts. The problem is she takes on too much and now feels shattered. Her publisher awaits her new novel. The TV scripts are running late. 'They're based on my novel, so adapting it is a piece of piss, if I had the time. The novel is called Kisses, Dreams and Amphetamines. I just need four clear months to finish it off, but I haven't had four clear months ahead since I was 12. It's the television that's taking up so much time. Yesterday I was in LA filming. When it finishes, I'll have a holiday. I haven't had one since I was 14.'
Wouldn't it be better to give up the television? It's not, er, as if your performances are totally brilliant. And anyway, television is a director's medium, with presenters having very little control.
'I'm giving up TV for ever when I'm 22. Writing is the best thing. You can do that at home with greasy hair. But to get the best money for your writing, it helps to be famous, and TV does that.'
But with your talents, you could exist on one column a week. 'No chance. My talent needs drugs and booze to support it.'
She is trying to live a more sensible life - till the present television series finishes. Last year she was smoking 200 cigarettes a day - now it's down to 40 - and drinking a bottle of vodka. 'I did have a couple of nervous breakdowns, hiding under the bed, scared to leave the house. I was getting smashed and stoned out of my head most evenings, standing on tables, waiting to get shagged.
'I remember at the Groucho Club one evening, totally gone, waiting for this boy I fancied. 'Are you going to screw me now?' I asked him. He said, actually, he'd like to do it in his own little bed. I said I haven't got the time for that, I'm going home . . .'
Taylor reappeared, still looking for the lost cheques. 'Try the basket,' suggested Caitlin. 'I remember taking one of them out of my bra and folding it up. Or look in the bathroom.' Taylor said he wasn't looking in the friggin' bathroom. (I went into it later - the bath was full of stagnant water and the ceiling had come down.)
Taylor is a pop-music writer, but not doing quite as well as Caitlin. 'He's lived with me for two months,' she said as he went off hunting again. 'We're getting married tomorrow. That's a joke. No, he's really great. My whorish days are over. Until now I've put up with blokes who are so stupid I've wanted to smash their heads in after two minutes, but they've been good in bed. Taylor's good at both. He's also got some brilliant jackets which he lets me wear.'
At the ancient age of 19, it seems surprising that she is still so obsessed by pop music, when she's seen so much, done so much - and, anyway, pop music is dead. 'Not that old one. I've written at least five columns explaining why it's not dead. Youth culture is not as important today because of demographic reasons. There are fewer teenagers, and they've no money. But the quality is still there. It's just that commercially they can't make a living. I can name you 10 groups who are absolutely brilliant. Mark Eitzel of American Music Club is a genius. So is Courtney Love of Hole. And Jim Shaw of The Cranes. It was always my ambition in life to meet these people, and I've now met most of them.'
Any other ambitions achieved, petal? 'Well, I've bought my parents a car - a camper van, actually. And I paid for Christmas dinner and bought presents. I can't buy them anything else at present, till we find these cheques . . .'
How about writing ambitions? Two decades ago, Julie Burchill was the great young female hope, with a similar background, non-university, writing for the music press. Now look at her. Making money, but not progress.
'I'm seeing the editor of a Sunday newspaper this afternoon. I know she'll offer me mega-bucks to do an opinion column, but I don't want that. I don't like opinion journalism. Anyway, how can you have 52 opinions a year? I'd like to do some interviews. How much do you get paid?
'I think I'll give it another 10 years, then I'll leave London for good. I want to live by the seaside, and have lots of children and a really huge Aga . . .'