Is it possible that an english student, 18 years old, write "he have now" (instead of "He has now")? I know it's an error, but I don't know if any english native speaker could make such an error. Thanks
No one's perfect. You should check this article about celebrity tweets that were corrected by young Brazilian students for its grammatical errors http://tambaytadiri.blogspot.com/2014/01/celebrity-tweets-corrected-by-young.html. These celebrities include Rihanna, Justin Bieber and Kim Kardashian.