We're still working on/with our son, at 25. He was wholly unprepared for the prestigious school he was accepted at, and was over by day 5. He wasted 2 semesters at comm college, and we stopped paying. He worked for our SMALL family mfg business since he was old enough to work, and has been in and out every since, but mostly out now.
We kicked him out of the house at about 20 as we were done with his attitude and complete and total disrespect for us. His entire life he's been disrespectful to us, yet we still hear what a great kid he is/was from most everyone else. He stayed with a friend a few days then moved in with my ex-step-mother (long story in itself!), and stayed in the room I grew up in for about 3 years till a major repair had to be done on the house that required a wall to be partly removed in his room. At that point we agreed to allow him back home, with very specific requirements and timelines. None have been met yet, but he's now finally acknowledged he's got issues he needs to resolve.
Many of his friends are still at home, although some are still in school. None of them seem to have much direction, and oddly enough very few (of the guys) have girlfriends. They don't seem interested. I think a girlfriend could do him a world of good, with 1 exception.... His prom date is still single (with a college degree), and one of the crowd, but he's not interested.
We fully believe that the whole social media/online world has polluted his mind in so many ways. He will argue to 'the death' over issues/things/solutions he read online, even when I have in depth experience with them. Not to brag, but I can do almost anything I want to, and do it well - home repair/maint/rebuilt/add, mechanical/electrical/electronics stuff (I built our mfg business from the ground up almost single handed, AND have a full time high end IT job). So, I know a thing or 2, and run circles around my brother at our mfg business daily. I built a large bronze casting furnace for a maritime museum so they can do their own casting and classes/seminars, and rebuilt an old wooden boat (and it's engines). I learn/study/research much of this on the internet, and that is a key difference between what he gets from it, vs what I get from it. I also learned a lot from my father (an engineer). I've tried to engage my son on all this his entire life, but he simply never had any interest in any of it.
By 22 I was a 'qualified' by the Navy to operate a nuclear reactor, and did so in training. I chose not to stay in the Navy though. My drive and responsibility got me there, and where I am today. He has neither. My wife an I joke regularly that he should have been my brothers son, as they are FAR more alike than I am with either.
He and I have managed a fairly good relationship as long as he does not ask me my opinion or questions about anything. That leads to an argument most of the time as he always insists I'm wrong and will defend his position regardless of how wrong he might be, even when others tell him so. He's never gotten into any major trouble, stopped by police a few times, but nothing more than a speeding ticket (once).
We hope we may have reached a critical point with him recently. After yet another battle a few months ago at the business, I informed him yet again, that it's time to go. He worked a couple odd jobs, then had an emotional meltdown that he's going no-where in life. Hello, we've been trying to get you to realize that for 5+ years.... So now hes on some medication, and I'm trying my best to not allow him to suck me into arguments. He battled this at first, but we convinced him to stay with it long enough for it to start working. 'I was reading online about the side effects...', argh.
Our daughter (2 yrs older) is the total opposite. She left for college, and never came back. Since then she married (but did not work out), got a Masters in accounting (while working), and now has a great job. Shes got her issues too (hence the divorce, and medicated now), but very different from our son. But then I admit that so do I (and my wife). Don't we all? We know how to manage them, and that's a key difference with him so far.
Best of luck with your situation.