Why your dog isn't the age you think

I'm assuming the 7 year thing is more of a rule of thumb for estimating age based on an 'average' human life. So if an average person lives to 84, then 84/7 = 12 which is around the average age for a dog to live. It kinda breaks down based off breed though. Some breeds are much more prone to issues that mean a closer to 8 year life span, and some can live to 20 easily. So it's more of a folk tale rule of thumb than an actual science.