This article is from the American Pit Bull Terriers Breed FAQ, by Michael Bur with numerous contributions by others.
On the whole, the APBT are a very healthy, robust breed. They usually
do well at the vets, because they are not threatened too easily and
have a high threshhold for pain. My sister, who is a veternian
technician and has handled thousands of dogs, said that the easiest
breeds to work with/on are the Labrador Retreiver and the Pit Bull.
The only health problem that I am aware of in certain lines is
demotectic mange. This can be treated with baths and topical ointment.
As far as life span in concerned, 12-13 years is probably about average,
although a 15-16 year old APBT is not unheard of.