My 4 yr old daughter will be five in November. She was diagnosed with Asperger's at an extremely early age. We just ended up being very fortunate. She was diagnosed at 18 months. I know they typically say that children can't be given this diagnosis until the age of at least 2 or 3, but as I said, we were very fortunate.
I'm not sure how much info you have on Asperger's, but we have made incredible improvements, to the point that people can't believe that Maddie ever had a problem. Some of my friends who have known me for awhile, marvel at what an incredible transition that has taken place right before their eyes. We put Maddie on a gluten free diet and that was a huge step for her improvement. (That is not to say that this would be the answer for your son, but it worked for us.)
I think homeschooling gives you an incredible advantage in so many areas for children, especially those with special needs. Children with Asperger's have been known to be incredibly artistically and mathematically gifted. In fact, they say that Albert Einstein possibly had Asperger's. Homeschooling will really give you an incredible opportunity for discovering your son's gifts and being able to focus on them - regardless of whether he is diagnosed or not.
My son began therapy for "autism behaviors" at 15 month old. Ten years ago. He was too young for a full dx at the time, but he did begin therapies to help him with functionality. He later got a dx of Autism and continued improving his abilities through therapy until he was about 6 when his dx was changed to Aspergers or High-Functioning Autsim, depending on who you talk too. He is a pretty typical Aspie, with the exeption of the fact that he is non-aggressive, which is not necessarily a trait of aspergers as much as it is the assumtion of society to think that all Aspergers people are aggressive. Anyway.... Im babbling!!
He has homeschooled for almost 6 years now and loves it. I love it and it is by far the best things we ever did for him. He is happy , successful, confident and surrounded by friends and people who want to see him succeed. When asked by others what is the number 1 thing that has helped him to do so well, I always say homeschooling.
Our son was also diagnosed with Asperger's, here in Albuquerque, when he was three years old. He is now 7 years old, and, it turns out, does not have Asperger's at all, according to three other doctors, including the president of the pediatric neuropsychology board of America. I recommend that we all take these diagnoses with massive grains of salt, and get second and third opinions. The medical establishment and school systems are much too quick to diagnose Asperger's, especially in very young children. In our case, our son turned out to be very bright, and gifted kids are often mistaken for Asperger's kids at an early age. Please trust your gut instinct on this. Do your research. Do not blindly accept what the doctors say because doctors are often wrong - especially if there is a check from a pharmaceutical company involved.