Twitter Help Center | Following Rules and Best Practices

To learn more about following, please read "FAQs About Following." What are the limits? We don't limit the number of followers you can have. However, we do monitor how aggressively users follow other users. We try to make sure that none of our limits restrain reasonable usage, and will not affect most Twitter users.

https://support.twitter.com/articles/68916-following-rules-and-best-practices