At 91 years of age and after more than half a century working as an editor for some of the greatest writers of the modern age, Diana Athill has won one of Britain’s top literary awards.

Her frank memoir, Somewhere Towards the End, was voted the best biography of the year at the Costa Book Awards yesterday and will join the winners of four other categories on the shortlist for the Book of the Year Award, to be announced later this month.

A week after being appointed OBE in the New Year’s Honours List, Athill has become the oldest winner of the Costa Awards, formerly the Whitbread, since they were established in 1971. She was honoured for her account of living with old age after a remarkable career as editor to Norman Mailer, John Updike, V. S. Naipaul and other luminaries of 20th-century literature.

After more than 50 years editing the work of others, Athill was in her 80s before receiving critical acclaim for her own writing, with the publication of her career memoirs in Stet in 2000.

Somewhere Towards the End talks with intimate honesty about friendship, love, sex and sore feet, reflecting on lessons learnt from a life well lived – a life nearing its end, as she admits without fear.

The judges described the work as: “A perfect memoir of old age – candid, detailed, charming, totally lacking in self-pity or sentimentality and above all, beautifully, beautifully written.”

Athill is third favourite for the title of Book of the Year at 4-1 with William Hill.

The category winners each receive £5,000, and their works will be scrutinised again by a panel of judges chaired by The Times columnist Matthew Parris and including the broadcaster Michael Buerk, the poet Roger McGough, the comedian Alexander Armstrong, the actress Rosamund Pike and a member of the public chosen in a competition.

The favourite for the prize is Sebastian Barry, who won the Novel category for The Secret Scripture, three months after missing out on the Man Booker Prize for Fiction.

Barry’s novel centres on Roseanne McNulty, a nonagenarian who has to cope with the imminent closure of the mental hospital where she has spent much of her adult life. The category judges made clear that it was their favourite for the grand prize, saying: “This exquisitely written love story takes you on an unforgettable journey – you won’t read a better book this year.”

Barry told The Times: “To be able to put the Costa Novel Award on your book is a matter of enormous pride – it’s a surprise and I’m overwhelmed.”

The outsider in the betting for Book of the Year is the Children’s Book Award winner Just Henry at 5-1, a new work by Michelle Magorian, the author of Goodnight Mister Tom.

Sadie Jones’s debut novel The Outcast won the First Novel Award, and is second favourite at 5-2 to win the overall prize after a year in which it was shortlisted for the Orange Prize and serialised on BBC Radio 4.

Adam Foulds, who won the 2008 Sunday Times Young Writer of the Year award for his novel The Truth About These Strange Times, took the Poetry Award for The Broken Word, and finds himself 9-2 to win Book of the Year.

Janine Cook, of the booksellers Water-stone’s, said: “This is an extraordinarily powerful list, a great start to the new year for readers.”

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