I was 64 when I was assessed and the Adult Autism Assessment was kind of fun! Remember that they usually assess kids.
I recommend just going for the assessment and being as cooperative as you can. You are the "patient", it is their job to know about the assessment.
I took copies of a bunch of personal records (report cards and stuff). I don't know if the Psychologist who assessed me looked at much but I'm sure she at least skimmed over the "baby book" my Mom compiled when I was a baby. I guess it was one way to get insights about me as a baby even though my Mom is long deceased.
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When diagnosed I bought champagne!
I finally knew why people were strange.