Contrary to popular belief, one cat year does not equal seven human years. In fact, feline aging is much more rapid during the first two years of life. A cat will reach the approximate human age of 15 during its first year, then 24 at age 2. Each year thereafter, a cat ages approximately four cat years for every calendar year. Thus, a cat who is 5 in cat years would be approx 36 in human years. But, take note that cats who live outdoor ages far more quickly than an indoor cat.
Refer to this chart for a better understanding of cat years to human years: