Try some simple steps first. Write out some goals in life. Choose a dream job and see if it's possible. Contact people who work in that field. The choose a more likely job and look into it. Then consider the worst case of what he wants in life at the minimum. I wish I'd thought it through instead of just doing through life without a plan.

What does it seem like he’s passionate about? If you know, great, if not, ask him what he’d like to study. Maybe he could start to take a couple of classes at a community college.

Severe anxiety and depression is very common amongst the ASD kids. It is mainly brought on my therapies. PTSD is common for those who have had ABA. That being said, what areas does he need help?