By their teens at the latest, every US citizen knows that they have rights. Students currently taking Civics class may even be familiar with what some of them actually are.
One of my pet peeves is that we are constantly told how critical it is that every person of voting age absolutely MUST vote and that increasing voter participation of itself makes a democracy better. Every citizen has a right to vote, however, if our government is to be of the people and BY the people, individuals exercising that right have just as much a duty to be informed on basic principles impacting our nation as do those they vote for. An uninformed vote is at best like guessing on your SAT's - except that your test scores affect everyone around you.
While clearly not on par with the first two, I'd highly recommend Thomas Sowell's Basic Economics to stay informed when it comes to determining which economic policies canditates and those in office support.