Talent + drive (obsession) + lots and lots of free-time.
Most of these types cut their teeth in their younger days - doesn't really mater if it is sports, musical instruments, art, coding, or whatever. If you spend 6-12 hours a day doing something, seven days a week, from you're 10 years old - you'll be pretty damn fantastic by the time you're college aged.
Yup, and you have to be pretty lucky to hit the nail in the head on your choice of vocation and profession.
A lot of people diversify, which is good for the mind, but bad if you have to compete for success.
Other people choose very unforgiving fields: want to live a life playing the guitar? Tough luck.
Some other people realize they don't like a hobby or job past some point, but turning over decades of skill to start a new path places them in a huge disadvantage.
It's not a person's fault to not choose the right career path when they're naturally too young to foresee their future in the field.
I personally feel pretty lucky to have chosen computers and technology for my vocation. If, for any chance in life, were to choose anything different when I was 12, then my life would have been entierly different.
She did right up until earlier this year and she just got her bachelor's a couple of months ago (all according to her public resume). Crazy stuff, awesome to see.