The average life expectancy of a Staffordshire Bull Terrier, which is a medium sized kind of dog is 12 to 14 years.Keep in mind that this is an average estimate some could l â¦ ive longer or shorter depending on a number of things such as; health, history, weight, activity level, personality etc.ulls can live to 10 to 14 years of age, but most are culled or slaughtered for beef when they're around 5 to 6 years old.