Who coined the term dog years? and who figured out the math that 1 human year was 7 dog years?

and if they judged it by the average life expectancy of a human compared against the average life expectancy of a dog and came up with the fact that 1 human year was 7 dog years. wouldnt that have changed by now. human life expectancy is way different than it was when they decided that. which im uming had to have been at least over 100 years ago.