Download Article When we talk about autism (which we are doing often during Autism Awareness Month), we tend to talk about children and ways that their parents can help. But children grow, and the parents of autistic children become parents of autistic adults, a role that is less defined and less discussed. In a guest blog today, Laura Shumaker, author of “A Regular Guy: Growing Up With Autism,” describes one weekend with her grown son Matthew, navigating the changing rules one interaction at a time.   THE PARTY By LAURA SHUMAKER When I pulled into the parking lot of my 23-year-old son’s home near Santa Cruz, Calif., he was standing there with his head cocked impatiently. “You said you would be here at 12 noon,…