There are two types of dependents, "Qualifying Children"(QC) and Other ("Qualifying Relative" 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.
Since he is over 23, you only claim him as a Qualifying Relative if he has less than $4300 of gross income (not just earned income). You must also have provided more than half his support. If he qualifies as your dependent, then you also claim the tuition credit.
In the TurboTax TT) interview, when TT detects his age, it will ask both the income and support questions to see if he qualifies as your dependent. In past years (when he was under age24), it did not ask those questions (there was a slightly different support question).
