How do you determine if full-time student? 1098-T says at least part-time. He was enrolled in college 12-15 hours a semester for each semester?

He was enrolled in 12-15 hours college for both Fall and Spring semesters.  The 1098-T states he was at least a part time student.  However TurboTax asks if he was a full-time student, how do I answer this?

My son is 23 years old and worked over the summer earning $10,800.  Does he need to file a tax return?  I provided more than half of his support.