There should be a government program to handle situations like this if there aren’t. Take an assessment of their current skills and interests and get them into employment and/or training for something that fits. You basically need to intervene when the parents won’t and do it in a way that’s as least stressful for the person as possible. It would pay off in the end because otherwise this person may end up on government assistance later when they most need it. Politicians who can pull this off may get to claim to have reduced unemployment in their reelection campaign. And it’s just a good thing to do. Some people won’t take the initiative. You have to do it for them and hold their hand.
Edit: As far as I can tell, the closest thing to this in the US is the one-stop centers. Each state has their own.
That’s the problem. The sort of person we’re talking about isn’t going to do this. What’s needed is an army of people incessantly knocking on doors offering to help.