How do you tell how old a kitten or cat is? Conventional wisdom holds that each year for a cat is equivalent to seven years of development and aging for a person. Or that each cat year is equivalent to five human years. Or that the first two years are equivalent to 21 years, and each subsequent year is equivalent to four or five years. Or that 20 years old in a cat is equivalent to 100 in a person.
Any time that conventional wisdom holds so many potentially contradictory views, you can count on the convention not to be especially wise. The many rules of thumb that are available to compare cat years to human years are usually based upon total life expectancy. An average cat’s life expectancy is around 17 years, and a human’s is around 84 years. This leads to a rough equivalency of five-to-one. But it is not an apples-to-apples comparison. Feline development and aging are not directly comparable to ours.
Nonetheless, feline development and aging are of great interest to anyone who has a cat. Most cats’ birthdays are not known exactly, and people are often curious about how to determine how old a kitten or cat is. It takes a significant amount of experience to get good at it, and different cats develop and age at different rates depending upon genetics and lifestyle. However, there are some rules of thumb that can help people estimate how old a kitten or cat is as well as know what to expect as their cat progresses through his or her life.
Birth to 1 week old: Kittens are born toothless and with their eyes closed. They spend almost all of their time during their first week of life rooting, suckling and sleeping.
1 week to 3 weeks old: Some kittens begin to open their eyes at around one week of age; most will have open eyes by two weeks of age. Generally they will remain toothless during this time. Their activity will still be quite limited during this time. The deciduous (baby) teeth begin to erupt at around three weeks of age.
3 weeks to 5 weeks old: The deciduous teeth continue to erupt through this time, and the canine teeth (the fangs) make their pointy appearance. Kittens become more active and engaged in their environments but they are significantly uncoordinated. They also become devastatingly cute. Most kittens will have blue eyes until they are at least five weeks old.
5 weeks to 8 weeks old: The baby teeth are fully erupted and individuals will be in full-on kitten mode. Coordination starts to improve. The eyes change to their adult color (unless the kitten is destined to be blue-eyed). Crucially, the prime window for socialization begins to close; kittens that have their first human contact after eight weeks may be harder to socialize.
8 weeks to 16 weeks old: This is prime kittenhood. It is a period of significant growth, play, and exploration. The deciduous teeth may appear to space out and be outgrown towards the end of this period. The deciduous teeth begin to fall out at around 16 weeks in most individuals, beginning at the front of the mouth and working symmetrically towards the back. The adult teeth begin erupt to replace the kitten teeth.
16 weeks to 7 months old: The adult teeth complete their eruption. Many kittens become more confident and assertive. Coordination improves significantly, and rapid growth occurs.
7 months to 18 months old: This period is equivalent to adolescence in humans. Puberty occurs in cats who have not been spayed or neutered. Cats reach their adult height and length, and then fill out to their healthy adult weight — and sometimes beyond it.
18 months to 3 years old: Young adulthood. These years are roughly equivalent to a human’s 20s. Health is generally good, and minimal signs of aging are noted. However, just as some twentysomething people start to show some signs of less-than-perfect health, some cats in this age range will develop dental calculus and gingivitis. Some cats also develop weight problems during this time.
3 years to 7 years old: Prime adulthood. Health problems (other than dental disease and obesity-related issues) are rare. Activity levels are still high. Cats remain agile and limber. However, most cats who don’t benefit from dental care (tooth brushing or regular professional dental work) will develop significant dental disease during this time.
7 years to 14 years old: This period roughly corresponds to middle age for cats. Cats in this group are not exactly old, but health problems such as kidney failure and hyperthyroidism may develop. The body will show signs of aging. The pupils of cats’ eyes generally develop a slight blue or grey tinge at around seven years of age; this becomes more prominent as cats age but it does not significantly compromise vision or quality of life. The hair may become less supple and may be noted to clump together. Dental disease will usually be pronounced in cats who have not received dental care. The bones become less flexible; owners of cats in this age range may notice that their pets’ ribs seem harder and less flexible. Signs of arthritis may develop.
14 years and beyond: Cats in this age group are senior citizens. The aging processes that began in middle age progress. Dental disease may become profound and teeth may fall out. The pupils of the eyes will have a significant grey tinge. Mobility may become compromised, and activity decreases. Clumping of the hair becomes more pronounced and may lead to matting. The bones will be brittle, and the ribs will be firm. Age-related illnesses such as kidney failure and cancer unfortunately become common. The voice may become noticeably raspy or hoarse. There may be evidence of hearing or vision loss, although poor eyesight is not generally related to the greying of the pupils.
Although the above guidelines apply to most cats, there are significant variations in aging rate among individuals. Much of the variation is genetic, but a substantial portion is lifestyle-dependent.
Here is an analogy. I used to work near a coffee shop. One of the shop’s regular patrons spent every afternoon basking in the sun and smoking cigarettes on the shop’s porch. She may have been 40 or she may have been 70; I couldn’t tell because her lifestyle had so ravaged her body. Similarly, five-year-old feral, intact, FIV positive cats who continuously fight may have rotten mouths and hair qualities that make them look 15 years old. Well-cared-for house cats can seem five years younger than they are.
Two of the leading concerns that occur as cats age are dental disease and mobility concerns. Regular dental care, through tooth brushing or regular professional dental work, helps to slow the aging of the mouth. Maintenance of a healthy weigh promotes flexibility and mobility and reduces the impact of arthritis.
Finally, infectious disease in cats can take a significant toll and contribute substantially to aging. Indoor cats are at lower risk than their outdoor counterparts, and indoor cats have longer life expectancies (on average) than their outdoor counterparts.
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Read more on the life span of cats on Catster.com: