Why are 90% percent of 13-14 year olds bratty or immature or jerks/douchebags.?

This is coming from someone who knows how to joke and laugh but not go all "thats what she said!" Why Are all 13-14 year olds like this, they act like theyre in 4rth grade. I was no way this immature at that age. I stopped making poop jokes back in probably 3rd grade and stopped saying girls had cooties in like 4rth but i still see kids like this now in late middleschool or early highschool. why is this?