Traditionally it has been said that one year in a cat is equivalent to 7 years in a human, but this statement is not completely accurate; In fact, some years of a cat's life are equivalent to more than 7 years and others are equivalent to less.
Additionally, not all cats develop in the same way. The biological age of the cat will depend on its genetics, nutrition, state of health, environment in which it is raised and level of stress to which it is exposed, etc. It will also depend on whether it is a purebred cat or a mix.
Notwithstanding the above, the following table indicates in general terms the approximate equivalences in years. Numbers in bold indicate that the cat is senior and in italics, imply that it is considered to have entered its senior years.