To find out what exactly goes with our beloved kittens who turn into full-grown cats in what feels like overnight, Bored Panda reached out to Kate Mornement, an applied animal behaviorist who runs a consulting agency “Pets Behaving Badly.”

Kate told us that generally, a cat is considered an adult and no longer a kitten at 12 months of age or on their 1st birthday. “Many cats are fully grown by this stage, but some breeds, like Maine Coons, aren't fully grown until 18 months to 2 years of age.”

When asked whether growing up fast is something specific to felines, Kate said that “I think this is true of all babies, whether they're human or animal!”

But puppies, just like kittens, grow very quickly also. “You tend to notice the growth more in larger breeds compared to smaller breeds and that's because it's more obvious. Most puppies are considered adults by 12 months; however, many of the large breed dogs, like Saint Bernards and Great Danes, will continue to grow until around 2 years of age.”

Every cat goes through a couple of age milestones until it turns into a fully matured king or queen mouser of the house. According to Nicole Fulcher, an assistant director of the Animal Medical Center of Mid-America, kittens usually stop growing up at around 12 months of age. It’s when their age is equivalent to a 15-year-old person.

However, that doesn’t mean they’re fully grown yet. In fact, your furry companion turns into a full-grown catto at 18 months of age, which is equivalent to a 21-year-old person, says Dr. Fulcher. Although most cats do indeed grow up at a fast rate, and it’s not your mind that’s deceiving you—some felines can take up to 2 years to reach their adult size.

Meanwhile, some of the key milestones for growing felines include: months 3-4 when baby teeth fall out and adult teeth appear; months 4-9 when kittens sexually mature; 1 year and more when kittens reach adulthood.

Only at 2+ years is the cat considered to be a socially and behaviorally mature animal and is fully ready for an independent life of its own. Meaning, they gotta spend their rest of pampered lives sitting on your lap and munching on chicken breast like there’s no tomorrow.