Autism spectrum disorder, from our limited understanding, is actually a 'developmental problem'. Which means that we believe that patients are actually born with it, but it is only later in life that we diagnose it.
We tend to find that infants who are autistic start to exhibit different behaviour compared to their peers since birth.
What early detection does, is that the family and the child is more ready to prepare for the future. Also there are autism programs that help the child learn how to cope with his/her issues early.
The earlier the psychological intervention, usually the better the outcomes.
But no matter what we do, or how hard we try, there doesn't seem to be a way to "reverse" autism spectrum disorder. That is, according to what we know at the moment.