Adolescents are developing their critical thinking skills from 11-17. During this time, they are critical of others and themselves. By age 20-25, they have tempered their critical ability with life experience, and by 30 have added wisdom and humility.
I think some people are so judgemental because they don't want to appreciate other people for who they are, without criticizing them. They could also be so judgemental because they are just mean to everyone who comes their way.
People are judgmental because they see the difference in other's and are either frightened by it or jealous of it for example you see someone walk into a class he looks disgusting in your opinion but is said to be a complete genius so you become worked up in wanting to find a flaw in this person but you can't you are frightened so you make fun of him being less natural to others this is you being scarred of him or you see him and want to surpass him but can't so you became jealous and once you are jealous it usually comes down to hatred of that said person easily judged by his knowledge and the way he look's it is only human nature. Hope this helped ^_^
Sometimes i feel like changing my attitude and say that i love critisizm and haters, so they cant critisize me without "comPlimentin me." :D then they dont want to say something good cause they really will be saying something kind to me!! :) i love it :)