A lot will depend on care. Especially in large breeds. One of my friends runs a Dane rescue. Danes are only supposed to live 5-6 years if I remember correctly. Hers average a life span of 9-11 years (barring extreme health issues) due to healthy diet and exceptional care. Large dogs definitely won't live as long as, say, a rat terrier but their life span can be significantly increased by buying from a responsible breeder who runs meticulous health tests and by providing detailed care. Also, the friend with the Dane rescue feeds raw.