See TaxMonkey's cite above.  "4 years of postsecondary education" are academic years, not calendar years.  Freshman, Sophomore, Junior and Senior.  If you have not completed the Senior year before 1/1/xx then this criteria is met.  (You still have the other ones, so often the "didn't claim AOTC for any 4 earlier tax years" becomes the limiting factor, even for Seniors.)