Actually the oldest dog on record was an Australian shepherd dog named Bluey. He was 29 years and 5 months old when he was put to sleep.
Mutts live longer than purebreds, too. Purebreds have a lot of health problems due to all of the inbreeding.
According to this article, dogs that resemble wolves will live longer. The sharper and more wolf-like the face the more likely it is to life a relatively long life. The flatter the face, the shorter the life span on average.
The link above gives an average lifespan by breed and lists common health problems with popular breeds as well.
Not all small breeds are guaranteed to live longer than large ones. A lot of small breeds have serious health problems, but so do some large breeds.
But it looks like on average the breeds they list on this site (which is no way all inclusive) that have the longest life span are mini poodles, bedlington terriers, toy poodles, dauchsunds, and whippets. Their average life span was all over 14 years.
I will say though, I recently had a dog who lived to be nearly 16 years old and he was a 75 pound shepherd/collie mutt. And my (American) yellow lab (their average life span is only 12.6 years) lived to be nearly 15 (American labs are much larger than English labs). He weighed around 100–110 pounds. We also believe he was a purebred.
My dads aunt had a husky who lived to be 21 (though he was blind and needed to be carried around at the end) and my friends mom had a German shepherd who lived to be 17. So there are exceptions.