Why do you think voting is a responsibility and not a duty

If you're suggesting that it be required by law (as in Australia) - - NO. That is not democracy. That is merely the state forcing citizens to go through a meaningless ritual in order to create a pretense of legitimacy.

Voting is a responsibility because, take Donald Trump for example (Sorry trump supporters), he says he wants to make america great again but he is trying to start a war, and if a child had the right to vote out of having a duty, s/he would vote for who ever even if they didn't know what they were trying to do to he country. So you have to be 18 + to vote so you know what you are voting for.