Autism is a highly complex and challenging condition and there is no one standardised treatment. That said, the very encouraging news is that there are a range of therapies that can help many of the challenges associated with autism.
Whilst the research shows that early intervention is more likely to have major positive effects, no matter the age of a person when they are diagnosed, people of all ages and levels of ability can often improve after receiving well-designed interventions. The key thing is, the sooner you get started the better. You can read more about autism therapies here.