There are two types of dependents, "Qualifying Children"(QC) and Other ("Qualifying Relative" (QR) in IRS parlance even though they don't have to actually be related). There is no income limit for a QC but there is an age limit, student status, a relationship test and residence test. Only a QC qualifies a taxpayer for the Earned Income Credit and the Child Tax Credit. They are interrelated but the rules are different for each.
The support test is different for each type. The support test, for a QC, is only that the child didn't provide more than half his own support. The support test for a Qualifying Relative is that the taxpayer provided more than half the relative's support.
Since your son turned 24, in 2025, he can no longer be you QC dependent, even though he was a full time student for 5 months. So, we next look at the QR rules. He must have had less than $5200 of income and you must have provided more than half his support for the whole year.
