There are two ways to be a dependent: to be a "qualifying child" or be a "qualifying dependent". The tests for each of these is different - please see Table 3-1 on page 25 in Pub 17. Yes, this is Pub 17 for 2018 because the IRS has not released the one for 2019 yet, but the tests are substantially the same.
To be a qualifying child, there is not income test; there is only "The child must not have provided more than half of his or her own support for the year." To determine if you provided more than half the child's support, please see Worksheet 3-1 Worksheet for Determining Support on page 28 at the link above.
There IS an income test to be a qualifying relative, and if your 22-year-old son was not a full-time student for at least 5 months in 2019, then this is the set of tests you will have to satisfy in order to claim him as a dependent. Obviously, though, he would fail the income test to be a qualifying relative because he made well more than $4,200 (the 2019 amount).
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