The adult symptoms of autism are the same as in children.

Some people can aquire autistic-like symptoms after an extremely (and I mean EXTREMELY) stressful/frightening experience, but never autism itself.

However, a person can be autistic for their whole life, and only diagnosed in late teens/adulthood because they weren't really that obvious.

If autism is initiating itself during teen years, this further leads me to believe that autism is caused by environmental factors.

Autism symptoms in adults are the same as those in children.

varying difficulty in verbal communications
difficulty establishing friendships
lack of empathy
preoccupation with one subject or interest
a need for routine
body rocking
hand flapping

Try going to the Autism Society of America for the answers…here the link:
autism-society.org/site/PageServer

I thought it's something that you're born with. I've worked with autistic adults and it's very apparent that they had a disability.