Certain genetic disorders that cause ID are known to shorten life expectancy, but Autism is not one of these. If you had Down Syndrome, the answer would be yes, because the extra chromosome causes damage to the internal organs of the body, and as a result, those who get born with it tend to have their lifespans shortened by 10 to 15 years.

you'll have to pore over a lot of medical literature for that one.  Even as husband of Professor of Special Education these past 32 years, i've never seen any discussion of how mild to moderate autism differs in this respect.  suggest you ask your physician for references to the literature or journals as place to start.  and do a LOT of internet searching.