LYNDA La Plante turns 80 next year - but she's calling this decade "the new 50s".
"There's this slew of incredibly old actresses treading the boards, there's the wonderful Glenda Jackson, 85, doing King Lear, and you think, are we the new 50s?" she says.
"There's Amanda Barrie, 86 going to India with Miriam Margolyes, 80 [for The Real Marigold Hotel series]. The wonderful actress from Widows, Ann Mitchell, going off to Hungary to make a movie and she's 82. And it's like, we're the new 50s."
The bestselling crime author of no fewer than 40 novels - including Cold Shoulder and Above Suspicion, as well as the hit TV series Prime Suspect starring Dame Helen Mirren - says there's "no way" she would retire.
"I'll continue to do it until I drop off the earth. Because I'm still learning new things all the time. I love it, it's very exciting, it occupies my brain," she says, adding: "All my friends are the same. I think mental health is absolutely connected to my work. It keeps you very mentally alert."
And physically, she feels great too. "I'm one of those who gets up and about, I get up at 6am every morning," she says - despite suffering from insomnia sometimes (the middle of the night is often when she "works the plot out" for her novels).
The 79-year-old's latest book, Vanished, is the third in the Jack Warr detective series, starts off "a rather irritable investigation of an eccentric lady" and ends up being a murder investigation and hunt for a suspect who appears to vanish into thin air.
A certain amount of solitude is all part and parcel of being a novelist, but for La Plante, that doesn't mean silence: "When I'm working, I'm energised, talking, being the characters, I'm laughing, crying, I act it out. Sometimes people have walked in and been quite shocked."
The process of writing can bring up surprising, and sometimes painful, parts of her own life.
"You use things in your own life, and you suddenly realise you're writing a little section or segment of your life that you hadn't paid much attention to.
"An ectopic pregnancy suddenly appears in the new novel I'm writing, and I remember clearly, I mean, I didn't know what it was." La Plante became a mum at 57, after many years of fertility treatments, going through the menopause at 32 and a divorce, when she adopted her son, Lorcan, now 18 (who still lives with her in Richmond, London).
You might think the creation of dark plots, often involving murderous psychopaths, violent crime, drug dealers, steely detectives and intricate forensic evidence (all devised with rigorous real-world research) would take its toll mentally, but La Plante is adamant it doesn't affect her. "I'm able to lift it with humour," she says.
Plus, "every novel written has a learning curve" - and that's what really drives her. She also hosts a podcast called Listening To The Dead, in which she talks to scientists she's worked with for research over the years.
"It's a very informative podcast for people interested in crime. You can hear me learning, still asking questions about blood splatter and forensic details and fibres."
Her chosen method of switching off from crime might surprise people though.
"I watch very odd programmes - like My 600-lb Life [a weight loss show on TLC]. I am an avid watcher. There's something absolutely exquisite about how they have fought for their lives, and you go through therapy with them," she says.
"Another one I like is Curvy Brides' [Boutique, also TLC]. I love it. The two women that run Curvy Brides' are so therapeutic, they're so warm and understanding."
When it comes to looking after her own diet, she doesn't want to waste lots of time cooking.
"One of the biggest things in my life is finding the chicken that cooks itself in the bag," she says, laughing. "I try to eat one good meal a day, I'm obsessed with green beans, I eat a lot of green beans."
Walking her enormous dog Hugo, a Borzoi, is her only form of exercise and brings her a huge amount of happiness. But his battle for his life has dominated La Plante's for the past year - he's been in and our of surgery for a punctured lung after swallowing pampas grass.
"I cannot believe this dog has created so much emotion in me, so many tears, so many prayers. All the dogs I've had in my life, nothing compares to this one creature - he's so gentle, and so loving," she says. "And now he's eating like a starving donkey but he's back."
So what does it take to look as fabulous as La Plante at 79 (apart from dog walks and green beans)?
"I bang on a bit of Nivea or whatever," she says, when asked if she has a strict skincare regime - and she hasn't been to a hairdresser in 20-30 years. "My sister cuts my hair," she laughs, holding her enviably thick blonde tresses.
"She lobbed off four inches. I said, 'I just wanted a trim, what have you done?'"
La Plante even does her own highlights: "You know when you see them with the tin foil? I thought, 'I can do that.' So I went to Sainsbury's, bought the foil, bought the peroxide, mixed it up. I did about two with tin foil and thought, 'Oh, this is very boring', so I got the toothbrush.
"So I have very, very minor beauty aids of any description. You could pump me full of Botox and I still have a little wizened face, so what is the point?" she jokes. "The only thing that I occasionally have is a wonderful massage."
Vanished by Lynda La Plante is published by Zaffre, priced £18.99 in hardback. Available now.
