poll tests have always eventually been reeled back because they are viewed as either unfair or, which would definitely happen in an economics related test, skewed too much towards one economic belief system. While blademage and I may both have entirely different economic viewpoints, I think we would both respect the right of the other to vote as we saw fit.
If the voting age were to be lowered I believe you have to either do it all the way or not at all. Those tests in themselves would be seen as belittling. That all said, I don't believe the voting age should be lowered. I did when I was 16 because I considered myself, and was, significantly more well informed than most my age. However, I still wasn't really prepared, and many people in that age range are going to be subject to heavy influence from parents and peer groups, even more so than with university students. There will always be exceptions and certain teenagers who have constructive things to add to the global discourse, but a line has to made somewhere.
As to free Marijuana, what? I'm placing the burden on you here to make a case for it before I bother writing one against it.