Some people suggest that cats age differently through their lives:

CAT AGE HUMAN AGE 1 month 5-6 months 2 months 9-10 months 3 months 2-3 years 4 months 5-6 years 5 months 8-9 years 6 months 14 years 7 months 15 years 8 months 16 years 1 year 18 years 2 years 25 years 3 years 30 years 4 years 35 years 5 years 38-40 years 6 years 42-44 years 7 years 45 years 8 years 48 years 9 years 55 years 10 years 60 years 11 years 62 years 12 years 65 years 13 years 68 years 14 years 72 years 15 years 74 years 16 years 76 years 17 years 78 years 18 years 80 years

adapted from Simon & Schuster's Guide to Cats ©1983