Most writers who are successfully published later in life seem to have been working at it for years/decades prior. Richard Adams, who published "Watership Down" in his 50s, may be the closest thing to a successful "newbie" who emerged later in life:
> Adams was 52 and working for the civil service when his daughters began pleading with him to tell them a story on the drive to school. “I had been put on the spot and I started off, ‘Once there were two rabbits called Hazel and Fiver.’ And I just took it on from there.” Extraordinarily, he had never written a word of fiction before, but once he’d seen the story through to the end, his daughters said it was “too good to waste, Daddy, you ought to write that down”.
Lee Child, author of the Jack Reacher novels, published his first novel at age 43, which he only started writing after being laid off as a television producer.
> Adams was 52 and working for the civil service when his daughters began pleading with him to tell them a story on the drive to school. “I had been put on the spot and I started off, ‘Once there were two rabbits called Hazel and Fiver.’ And I just took it on from there.” Extraordinarily, he had never written a word of fiction before, but once he’d seen the story through to the end, his daughters said it was “too good to waste, Daddy, you ought to write that down”.
https://www.theguardian.com/books/2015/jan/04/richard-adams-...