It all depends on when they were weaned when younger. For some, when they get older, around 9 weeks old, they already calm down. In contrast, when they start playing and when it's time for sleeping, others will still be a little hyper sometimes when getting older (usually this happens when the cat is an only child without siblings and isn't socialized with other pets). Most kittens will begin to calm down between 8-12 months old.