Whatever his motivation, if he wants to attend college, and can, he should. Have you thought of Vocational Rehabilitation? (A federal agency) In some states this is available to people of all ages with a disability. (Special Education qualifies you, autism spectrum generally does.) One applies to Voc Rehab. They have you assessed. Then you do or don't qualify. If you do, they work to make you employable. For some it is assistance getting a job, keeping a job. Others it is getting a license, getting tools. For others it is training, and still others - it is college and related expenses. I'd check it out. It could provide your brother with the assistance he need to get going and to be successful. They will do job coaching as well. Most colleges have learning labs available to students, as well as supports for people with disabilities. You just have to inquire. Taking fewer classes can help. 9 credits is an easier pace and generally allows you to keep your financial aid status. Sounds like your brother could use some support here navigating this. Just taking one class at a time helps one to adjust to college. Take the classes that are "fun".
It is never too late to go to college. My mother dropped out as a freshman and returned in her 40's, earning a BA and MA.
Help your brother find the support he needs.
Good luck to you both.