Your cute cat may forever seem like your little baby, no matter what her technical age is. However, when it comes to the eternal question of when exactly a kitten becomes an adult cat, some say around 6 months while others give it approximately a year or longer.
A big growth spurt tends to happen in kittens between 2 and 6 months. At around 6 months of age, kittens may start looking "adult-sized," although it always depends on the individual animal. It is important during this time frame to feed the little one frequent protein-packed meals, ideally about four times a day. Food that is formulated specifically for kitten consumption is ideal, as it contains the components necessary to keep them growing strong and healthy into full adulthood. After six months, most cats are fine eating adult cat food. To be certain, consult your veterinarian on when you should make the change.
When it comes to walking like an adult cat, this change tends to happen at a very tender age. When the little fluff balls hit about 6 weeks, they are rather suddenly able to run and walk around just like grown-up cats. This time period is also key for kitten coordination development. Kitties start to love fiddling around with things and playing with random objects at this time -- excellent for stimulating and expanding their minds. Just be sure to always monitor what your precious pet is handling, for safety purposes.
When kittens are about 5 or 6 months old, they essentially are teenagers -- watch out! Most kittens reach full reproductive maturity around this time -- essentially their version of "adolescence." During this period, female cats usually start their heat cycles and male cats begin engaging in mating behavioral patterns -- think urine spraying, pacing, restless roaming and fighting. Though 5 to 6 months is typical for feline sexual maturity, some cats reach it much earlier, and some others take a lot longer.
All kittens are different and some mature a lot faster than others. However, in all aspects, you can usually safely say that a feline is fully developed by 18 months. By this stage, your fluff ball is essentially a "cat" in all senses of the word, from issues of dominance and bodily growth to sexual maturity and social interaction. Remember, though, that most spayed and neutered kittens never display typical mating behavioral patterns unless out of previously learned habit. Just don't tell them that they're not real adults!