刚Google了一下，具体数据如下：
The results:

Women over age 40 are 77% more likely than women under age 25 to have a child with autism.
Women over age 40 are 51% more likely than women aged 25-29 to have a child with autism.
Women aged 35-39 are 31% more likely than women aged 25-29 to have a child with autism.
Women aged 30-34 are 12% more likely than women aged 25-29 to have a child with autism.
Women under age 25 are 14% less likely than women aged 25-29 to have a child with autism.
Men over age 40 are twice as likely as men under age 25-29 to have a child with autism, but only if the mother is under age 25.

详情见
http://www.webmd.com/brain/autism/news/20100208/autism-risk-rises-with-mothers-age

但是CNN的评论也说，也许大龄妇女受教育程度高，所以对这方面的问题比较重视；而年轻女子糊里糊涂的，孩子有autism症状也不去看医生。所以也许对这组数据要discount一些。