None. If you can write, you can be a writer. You may not be any good at it and hence be a starving writer, but there's no actual requirement that you go to college (and no guarantee that going to college will help all that much anyway).
Becoming a 'professional writer' is a euphemism for a writer with published work to his or her credit.
Unless you want to become a journalist, or a screenwriter, or ghost writer for a corporate officer -- or some other kind of specialty writer -- you can write for publication so long as you have a story to tell and a command of the language in which you want to tell the story. You don't need a specific amount of schooling for that.
However, schooling in language and literature are are valuable if you want to be a writer. In this course work, you'll become familiar with genres, structure, character development, plot scenarios, nuances of language, and so forth. A liberal arts degree in a language proves your commitment to the career path, and gives you tools you can use to write better.
Principally, you can learn lots from simply reading. Read as much as you can.
2
Enough to at least spell college
It depends on how great you want to be because it takes long years to gain thinking skills to be a science writer=•=
You need 7 years of college.
5-7 years
nurses have 2 years of college
you need to go to college for 2 years
Models do not need college for their job.
3.4 years
2-4 years of college
8 to 10 years
You do not need to go to college to be a beekeeper. Many people do it as a hobby.
i would say about 4 years of college