There is a lot of good advice here, but I don't see the social contact part. Find others who are doing the same or similar so they have to interact with their peers. My now ex-wife and I homeschooled our autistic daughter. Hard but very satisfying job. She had a very hard time with social anything but we tried. She passed the GED when she was Sixteen and had her AA by eighteen.

Teens are tricky since few are self disciplined enough to work without supervision, and more likely to fire up a doobie and go online for porn.

But if any text book can be found online for free, and most top universities offer free online courses and even degrees. My home schooled kids used to take these for fun when they were still little, so there's no checking up on your age.

I taught early 17-24 year old early school leavers from 2010 to 2012, and now tutor/mentor the kids in this region who are enrolled in distance education. They come in once or twice a week to meet with a school co-ordinator, (thats not me). I just generally interact with them, and provide one on one help as needed for most subjects. I am mean, tough, sarcastic, pick on them all the time. They are not obligated to come in, and I help at their request. BUT ............... They know when I hassle them they get their work done. Kids are lazy, they like to be irresponsible, so they whinge amongst themselves that they HAVE to do their assignments and such because I make them. My foster son was the same.
My recommendation however, is if he can complete "normal" schooling, he should do so.