The four years for AOTC are four academic years or claimed for years on taxes.
To be eligible for AOTC, the student must: be pursuing a degree or other recognized education credential. Be enrolled at least half time for at least one academic period* beginning in the tax year. Not have finished the first four years of higher education at the beginning of the tax year.
If you are in a graduate program you cannot take AOTC but can file for Lifetime Learning Credit.
Based on the information provided it sounds like you are eligible to claim the AOTC.
AOTC
