Doctor Who boss Steven Moffat has said the casting of 50-something Peter Capaldi in the show's lead role will be no barrier to being "terribly boyish and young".
Moffat said handsome actors did not fit the bill for the Time Lord, preferring people who were "utterly compelling, attractive in a very odd way".
After the BBC1 show cast three successive younger doctors, Moffat turned to 56-year-old Capaldi, best known as Malcolm Tucker in The Thick Of It, to succeed Matt Smith, the youngest doctor, who was 26 when he was cast.
"I always thought Matt, while a very young man, had something of the demeanour of a much older man, whereas Peter is a man in his 50s but is terribly boyish and young at times," Moffat told the new issue of Radio Times.
"I like the doctors to have mixed messages about what age they are – you can't really pin them down," he said.
"The doctors are all the same doctor really, at the end of the day. And to emphasise the senior consultant over the medical student for once reminds people that he's actually a terrible old beast. Matt's method would do that … you'd think, 'You're not really a puppy are you?' Just like Peter Capaldi's doctor will sometimes remind me he's a big kid at heart."
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Moffat said he chose Capaldi because there was "something about Peter's demeanour, his eyes, his attitude – he's tremendously bright and that comes out on screen.
"When you choose a doctor you want somebody who is utterly compelling, attractive in a very odd way. None of the doctors are conventionally attractive, but they're all arresting. Handsome men don't quite suit."
He added: "Matt Smith's a young, good-looking bloke from one angle but is actually the strangest looking man from another. You need that oddity; you need somebody who is carved out of solid star."
Moffat described writing last year's 50th anniversary episode of Doctor Who as "terrifying", adding: "I can remember sitting with my wife saying, 'I can't tell if it's good any more, it could be rubbish - I'll have to leave the country. I'll have to fake my own death.'"