[Valpal1]

The mother is the “environment” for babies. There is already a well established link between maternal age and autism.

This article has a good overview. http://www.scientificamerican.com/article/autism-maternal-age/

[Black Agnes]

Then why is the ‘environment’ of a 40yr old mother different from the ‘environment’ of another 40yr old mother?

Unless the argument involves some sort of protective mechanism of early youth pregnancy ‘protecting’ the eggs somehow. In that case it’s ‘environmental’ and related to the chemical/biological process in question. And not age related.