Autism is generally viewed as a male disorder. One of the first google suggestions for a search on women and autism, in fact, is "can girls develop autism:" showing two common misconceptions at once. Portrayals of autism in media are overwhelmingly young and male. Asperger's Syndrome, a disorder on the high-functioning end of the spectrum, is generally associated with internet trolls- an overwhelmingly young and male group who like to use the term as a synonym for "jerk on the internet."
I was diagnosed with Asperger's when I was nineteen. I had been seeing psychologists for years for a variety of reasons, many of whom felt I had some sort of sensory disorder/developmental issue, but were reluctant to put an exact name to it because I don't fit all of the traditional criteria. Even now, I tend to identify as "autistic spectrum" rather than "Asperger's."
Late diagnosis (or no diagnosis) is very common for women. Girls on the spectrum often deal with society differently than boys, because society treats them differently. Girls are more likely than boys to do what I did during elementary school- mimic their peers, and hide their difficulties. Girls also may have different autism-related behaviors than boys- or be conditioned not to show those behaviors, such as repetitive movements, in front of others.
More research into this is needed- and more education. The way autism is diagnosed may need to be revamped.