When you see all of the great books for sale, it can be easy to assume that the author was born with the talent to write. While talent does play a part, that talent is only ten percent of the process.
Ninety percent of being able to write fiction comes from learning the skill and anyone at any age can learn how to write fiction and then sell it for a handsome profit online.
Research
Sometimes writers assume that because they're writing fiction, they can just make stuff up. This will only go so far because readers will suspend believability only to a certain point.
After that, they won't. If your research isn't correct, you'll have readers rolling their eyes and putting the book down. But worse than that, they'll tell others how off the research was and you'll see that reflected in bad reviews and low sales.