Kittens always look cute. Then they grow up and become cats. Just like kids that start acting uncontrollably when they become teenagers, so do cats start acting up when they hit their teenage years.
Males start spraying to mark their territory at this time while females often go into heat and may also urinate around the house to advertise herself as available, although it’s usually easier for the cat just to hang out in bars instead.
Expect cats to get more rambunctious, scratching everything in sight and getting more playfully aggressive. At least with cats, you don’t have to worry about them taking your car keys and wrecking your cat while you’re asleep one night. After dealing with howling cats, you might start believing it could be easier dealing with actual human teenagers instead.