The original answer given above stating that as long as you are not classified as a graduate student you can take the credit is not correct. Most schools don't classify someone as a graduate student until they have an undergraduate degree. Specifically for the Original Poster who said he had more than 120 credit hours, the requirement is that you cannot have completed 4 years worth of credits (as determined by the school). Most schools look at 120 hours as the completion of 4 years worth of credits and therefore eligible for graduation (assuming other criteria have been met), although the Original Poster would need to look at his own school's criteria.
Here is the actual criteria from the IRS along with the link...
Completion of first 4 years. A student has completed the first 4 years of postsecondary education if the institution at which the student is enrolled awards the student 4 years of academic credit at that institution for coursework completed by the student before 2015. This student generally wouldn't be an eligible student for purposes of the American opportunity credit.
Exception. Any academic credit awarded solely on the basis of the student's performance on proficiency examinations is disregarded in determining whether the student has completed 4 years of postsecondary education.
https://www.irs.gov/publications/p970/ch02.html
