Small breeds usually live up to 12 years. Large breeds is up to 7 years. The larger the breed, the less life span. It's best to get a mix breed because less health problems and better life spans. If you want to know more about all the breeds, please go to www.animalplanet.com and go to "Dogs 101". It says each breed and the history of them
I will add that smaller dogs can live a span on 10-15 years if treated right throughout their life. Larger dogs rarely get past 12. Some severely inbred dogs such as boxers, labs, bulldogs, and rottweilers usually have many health problems that result in early death. Of course, the overall health and care of the dog over its life will determine its longevity. A well vetted and fed dog can last a very long time.