G.T.
If he cant function on his own and handle money and regular daily responsibilites, they need to get him on social security disability... He'll then get a monthly income and can live in a group home surrounded with people like him and mentors to keep them on track, or his parents can still take care of him but have a little income coming in to help with expenses.
I'm a low income apartment manager. I have lots of people like him living here, they cant be left alone because they are vulnerable to people that like to take advantage of them.