The rates of smoking are much higher.
“While the prevalence of smoking in the total U.S. population is about 25 to 30 percent, the prevalence among people with schizophrenia is approximately three times as high - or almost 90%”
I think that smoking so much is one of the main things that really cuts down on the life span.
Aging has been defined before as: “the set of accumulated side effects from metabolism that eventually kills us”
Smoking increases metabolism.
That is in addition (in my opinion) to the damage smoking does to the lungs and heart.
“Research has shown that smoking increases heart rate, tightens major arteries, and can cause an irregular heart rhythm, all of which make your heart work harder. Smoking also raises blood pressure, which increases the risk of stroke.”
Schizophrenics seem to often die from heart disease.
“more than two thirds of patients with schizophrenia, compared with approximately one-half in the general population, die of coronary heart disease (CHD). The chief risk factors for this excess risk of death are cigarette smoking, obesity leading to dyslipidemia, insulin resistance and diabetes, and hypertension.”
I think that all of this leads to smoking as one of the main culprits for early death for those of us on antipsychotics.
I suppose we also shouldn’t overlook ‘obesity leading to dyslipidemia, insulin resistance and diabetes, and hypertension.’ But, seems to me that not smoking, combined with decent diet and exercise, might make a schizophrenic or others of us on antipsychotics live much longer. 
I guess the main issue is where to find the motivation to make these lifestyle changes with avolition or amotivation. 
I don’t know for certain. Maybe these websites can help: