The memory develops after birth. A baby starts by registering how it should move. From around the age of three, a child can register events which form part of its life story, to be recalled in later life. But emotional events such as traumas are possibly registered much earlier as stray facts. These can elicit reactions, although you can’t retell them.
The probability of having autism is greater for an individual if it runs in their family. This suggests hereditary factors. But what do you actually inherit? What you inherit is a predisposition for a specific development of your brain. This, together with what you experience while growing up, can lead to the development of a mild to severe form of autism.