My friend is 15, he still watches it, wears T-Shirts on it, and he always yells ADVENTURE TIME!
It is embarrassing as hell to be around him. People think he is mentally handicapped... It is just embarrassing for me to even be friends with him. I never talk with him except in classes that nobody would get annoyed with him.
So the moral of this story, is that if you watch Adventure Time, your life will die.
Don't
Watch
It.