Didn't he get his own place? Is he working and paying for that place? If he is in college full time, then he can work part time. What is the hurry to come back home. Is it to save money? I think it is important to know whether he can keep his job. When out stepdaughter moved back in at 19 she immediately stopped going to work, and went back to old ways of lying around doing nothing. It did not work for her to be home. She thought of it as a way to do nothing.
Each person is an individual. With her, we had her sign a written contract as to the rules of coming back. We ended up having to kick her back out.