It is commonly believed that one year of a cat's life is equivalent to seven years of a human's life. Scientists have discovered that the scale is not uniform at all. The first two years in the life of a cat is a period of rapid growth and is equivalent to 24 years of human life. After that, the growth slows down and each feline year becomes about four human years. The scale is shown in the following table:
So by the time Parker and Piper have their two-year-old (human years) birthdays early next year, they will be 24 years old in feline terms.