Adding to your equivalency note —
Based on actuarial (longevity) statistics, the following are the preferred calculations.
On average, cats live longer than dogs, and small dogs live longer than large dogs, but the following averages hold:
For both dogs and cats, the first 2 years total to 25 human years.
After that, each cat year = 3.5 human years and each dog year = 4 human years.
For example, a 26-year-old cat would be 109 and a 26-year-old dog would be 121.