5 Answers

The ability to spell

Based on the way you question is written, many many years WBMG   ;)

Plenty of hard work, and study, and dedication and sacrifice. And an innate knowledge of the subject that you want to become a professor of because as a professor you have to answer the questions of others on the subject and be able to teach, analyze and give it in its simplest form to any questioner of any age.

In Most American Institutions of Higher Learning you need a PhD or the equivalent to become a Full Professor. 

Education, dedication and love for young people. While on this site please scroll down. In the bottom right corner of the page, you will see the “Blog” tab. Click on it. Read as much as you can. You will learn a lot about who is in this site and what you can expect from it. Highly recommended reading is “Colleen on Hello akaQA members”.