There's a fairly new poster on JABS, who goes by the name of "Spambuster". He or she has made an interesting point:

As the average age of diagnosis of childhood autism is 3-4 [depending on which sources you use] and for Aspergers it is around 8 years old, this means that half the children of those average ages will not yet have been diagnosed.

If this is the case, how come anti-vaxers claim that parents can identify the very moment their child started regressing into autism? And that moment is always shortly after vaccination? Or do they write the moment on a calendar, then wait between two and seven years before taking any concerns to a doctor?