How to determine a dependent?

My son is 27 years old and just graduated med school in May. He obtained a full time position in June. At that time he no longer was a dependent of ours but on his own. We paid his college tuition for spring 2019 semester and have the 1098-T.  We can't claim him as a dependent or is there a way to have a dependent for only 5 months? What do I do with the 1098-T if he is not a dependent of ours and he did not make the payment? During the time he was in school, we also covered the cost of his apartment.