I second the advice from @Lys — his thirst for reading and knowledge is not a bad thing. Use that interest to get him active in other ways. Interest = Motivation for the ADHD brain.
Remember too, though, that social struggles are very common for individuals with ADHD and they often avoid social situations because of it. If you can get him involved in something he’s passionate about outside the home, he can meet like-minded people and that will ease the social awkwardness. Ultimately, he has to want to do this, as he’s an adult.
A job for the summer could really help him practice social skills and build confidence. Just make sure it’s not too far out of his comfort zone. Too much stress will make matters worse, not better.
ADDitude Community Moderator, Author & Mentor on Parenting ADHD, Mom to teen w/ ADHD, LDs, and autism