I'm slowly heading toward 50, and I have read and learned a lot about autism in my life - I had to understand it - there has not been a case ever to reverse autism. It may be subtle down with age, but autism, as far as I know, is a birth to death disability that is more visible on one than on others, depending on where they are on the spectrum.
Still, Autism is one of those things that we really don't know enough yet, so I say anything is possible as a rule.