The October 5 1950 edition of the Toronto Daily Star contained an article about an Australian novelist who wrote her first best-seller at the age of 16:
Catherine Gaskin (1929-2009) was a romance novelist. Wikipedia claims that she was 15 when she wrote This Other Eden and that it was published in 1947 when she was 17, not 16, but this is nit-picking. Either way, she was quite young when she first became successful.
Ms. Gaskin went on to write a total of 21 novels. Her most successful work, Sara Dane (1954), sold two million copies and became a TV mini-series in Australia. During her life, she spent time in London, Manhattan, the Virgin Islands, Ireland, and the Isle of Man, and then went back to Sydney, where she originally grew up. Hey, why not?