I was fortunate to be surrounded by people who work with autistic people, who pointed me in the right directions, and one had me pegged to the wall. I also took some assessments that had me clearly autistic. After I learned this, several were saying, "I always suspected that you..." or variants. The one that had me pegged to the wall works with teaching autistic children, and her reaction was, "He didn't know already?" There are ways to know definitively that do not cost much to find out.