When Do They Grow Up? The Age Cats Stop Being Kittens


Kittens go through several developmental stages as they grow from newborns to juveniles to adults. Knowing what to expect during each stage can help cat owners better understand their kitten’s needs and behaviors. Understanding kitten development is also useful for determining when a kitten transitions to an adult cat.

Defining the end of the kitten stage is important because it marks a shift to adulthood when cats become more independent and reach sexual maturity. Additionally, kittens have unique health, nutrition, socialization and care requirements compared to adult cats. By looking at physical, social and behavioral changes, cat owners can identify when their pet is no longer a kitten.

Physical Changes

Kittens go through many physical developments in their first weeks and months of life. According to Kitten Development Timeline: How to Tell How Old a Kitten Is from Elanco, kittens are born with their eyes closed and their ear canals closed. Their eyes typically open between 1-2 weeks of age and their ears open between 2-8 days of age. They are unsteady for the first couple of weeks, but by 3-4 weeks they can walk fairly well. Kittens start getting their baby teeth around 2-3 weeks old. According to the Hill’s Pet article Kitten’s Development Milestones: First Weeks & Months, kittens start getting their permanent teeth around 3-4 months old.

As outlined in the PetMD article Kitten Development: Understanding a Kitten’s Major Growth Milestones, motor skills and coordination quickly improve over the first 8 weeks. Newborn kittens have limited mobility, but by 4 weeks they can walk, run, and play fairly well. From 8-12 weeks, their coordination improves dramatically and they become quite nimble and agile.

So in summary, major physical developments like eyes and ears opening, teeth coming in, and motor skill coordination occur rapidly over the first 2-3 months of a kitten’s life.

Socialization Period

The most critical socialization period for kittens is between 2-7 weeks of age. During this time, kittens learn important behaviors and skills through interactions with their mother, littermates, and humans. As explained by VCA Hospitals, “The most sensitive period for socialization in kittens occurs when kittens are between two and seven weeks of age. During this period, kittens form social attachments and learn social skills and behaviors from their mother and littermates” (https://vcahospitals.com/know-your-pet/socialization-and-fear-prevention-in-kittens).

Kittens who are handled gently and frequently by humans during this period will become socialized to people. According to Nutrena, “The primary socialization window for kittens occurs from 2-7 weeks of age and a secondary one lasts from 9 weeks to 14-16 weeks. It starts with self-play and transitions to play with littermates” (https://www.nutrenaworld.com/blog/kitten-socialization). If kittens do not receive adequate socialization during this time, they are more likely to develop fear responses and behavior problems later in life.


Kittens begin the weaning process, transitioning from nursing to eating solid food, around 4-6 weeks of age (1). This is a crucial developmental stage, as kittens learn to incorporate solid foods into their diet and become less dependent on the mother’s milk. Weaning typically begins with the introduction of wet food, gruel, or kitten formula. As kittens grow accustomed to solid foods over 2-3 weeks, the mother will produce less milk and encourage the kittens to feed from solid sources. By around 8 weeks of age, kittens should be eating solid food completely and no longer nursing (1).

Proper weaning improves kittens’ nutrition, teaches independent feeding behaviors, and facilitates the separation process as kittens prepare for adoption or life with a new family. Allowing kittens to wean too early, before 4 weeks, or too late, beyond 8-10 weeks, can negatively impact health and development. With patience and proper techniques, cats can ensure their kittens wean successfully during this important transitional stage.

(1) https://keepingpet.com/weaning-kittens/


Kittens should begin receiving vaccinations between 6-8 weeks of age and receive booster shots every 3-4 weeks until they are 16 weeks old, according to PetMD. The core vaccines kittens need to protect against common feline viruses and diseases include:

  • Feline viral rhinotracheitis (herpesvirus)
  • Calicivirus
  • Panleukopenia

These are commonly combined into a single vaccine like the Feline Distemper Vaccine. Additional recommended vaccines may include feline leukemia and rabies. Kittens will require an initial dose of each vaccine followed by boosters at 3-4 week intervals until fully vaccinated at 16 weeks. The average cost for each kitten vaccination visit is $15-$25, so expect to budget $60-$100 for a complete kitten vaccination schedule according to Forbes. Full vaccination provides critical protection and prevents potentially fatal infectious diseases in kittens and cats.


The typical age for spaying or neutering a kitten is between 4-6 months old. Most veterinarians recommend spaying or neutering at this age before the kitten reaches sexual maturity, which is around 6-8 months old.

Spaying females involves removing the ovaries and uterus, while neutering males involves removing the testicles. This surgery prevents kittens from reproducing and having unwanted litters. It also provides health benefits like preventing certain cancers and infections.

According to the American Veterinary Medical Association (AVMA), pediatric spay/neuter of kittens as young as 8 weeks old is safe and may have advantages over traditional age spay/neuter. However, some veterinarians still prefer to wait until 4-6 months for the surgery.

By 4-6 months of age, kittens have developed sufficiently and the surgery is routine and low-risk. This age allows kittens to mature more while still preventing reproduction. It provides a good balance between health, behavior, and population control.

So while kittens reach sexual maturity around 6-8 months old, most veterinarians advise spay/neuter surgeries take place ideally between 4-6 months of age.




Kittens start becoming more independent around 12 weeks of age. According to PetMD, at 8 weeks old, kittens will have lots of energy and curiosity to explore their surroundings independently. Their coordination and agility are nearly fully developed at this stage.

As kittens reach 12-16 weeks old, they are gaining confidence and spending more time away from their littermates and mother. Their play skills and social abilities allow them to interact with other cats and people effectively. They are learning hunting behaviors and how to clean and groom themselves independently.

By 6-8 months old, kittens are becoming quite independent according to Chewy. They have perfected many social skills and are ready for responsibilities like flea, tick and heartworm prevention treatments. At this stage, they rely less on their mother and littermates for security and socialization.

While kittens continue maturing past 6-8 months, after 12 weeks they have gained much of the independence needed to explore, play, and learn on their own. Their rapid development from dependent newborns to curious, energetic felines is mostly complete by 12-16 weeks of age.

Adult Teeth

Kittens start getting their adult teeth around 3-4 months of age. The incisors are usually the first adult teeth to come in. By around 5-6 months of age, the premolar and molar teeth start coming in to replace the baby teeth. According to vcahospitals.com, kittens will have their full set of 30 adult teeth by around 6-7 months of age [1]. The baby teeth are gradually pushed out by the emerging permanent teeth and the roots are reabsorbed. Most kittens will have a mix of both baby and adult teeth as they go through this transition process.

Some signs that a kitten is teething and getting their adult teeth are drooling, reluctance to eat hard food, and chewing or biting on objects. Petmd.com notes that kittens may show some irritability or discomfort while they are teething their new adult teeth [2]. Providing chew toys and switching to soft food can help make a kitten more comfortable during this process. Once a kitten has all of their permanent adult teeth, they are done teething.


Around 6-10 months, kittens reach sexual maturity. This happens earlier in female cats, as early as 4 months, and later around 10 months for males. Sexual maturity is marked by cats going into heat and being able to reproduce. Female cats will have their first heat cycle, while male cats will start marking territory by spraying urine. Going into heat happens every 2-3 weeks and lasts around 4-6 days. This is a time when female cats actively seek male cats to mate. Spaying and neutering cats around 6 months helps prevent unwanted litters of kittens. Reaching sexual maturity is a clear sign that kittens have grown into adult cats.

According to Purina, cats are considered adults around 1-2 years old once they are reproductively mature and their full physical growth is complete. So the 6-10 month range is when they transition from kitten to adult in terms of sexual development.


In summary, a kitten typically becomes an adult cat around 12 months of age or older. While there is no definitive point when a kitten is suddenly considered an adult cat, the 12-month mark is a good general guideline. Around this age, kittens have reached their full size, completed key developmental milestones, established adult behaviors, and gained independence from their mother. While some cats may reach physical or social maturity slightly sooner or later, most kittens are full-grown adults by age 1. So while the exact age varies from cat to cat, after 12+ months, most owners can be confident their playful kitten has grown into an adult feline.

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