I think they are mostly stuck at about 13 or 14 years of age (mentally)...probably from beginning drug and alcohol use. They are still in rabid rebellion against everything, and still trying to prove that they're better and smarter than "the adults." (Or, as they say, "The Man" or the "Power" of truth to power.)
They still think Mommy and Daddy...or the world as a whole...owes them a living. They still think their opinions are positively perfect in every way. They still quake with fear over every little upset, because they know that they need someone bigger and badder to protect them...therefore, their worship of Socialist government.
I say this as a mother with 4 kids now past this stage...almost every liberal acts exactly like the worst stage of teenager.