Ok since BBC didn't want to say I will since the information is available. The oldest living dog is a Chihuahua mix in the US named Spike at 23 years and 327 days old. Your welcome
Most charts stop at 16, which shows how remarkable this is. As it's a curve not a straight line it's unclear if you can keep extrapolating but over 16 dogs seem to largely fall into the equivalent of people in their 80s.