What would be the issue of having a competence test rather than a voting age?

Well, the snippy answer is that it's unconstitutional. ;)

The practical but still snippy answer is that it's not practical, since no one would vote for any such legislation... even if it was well-thought-out, which it won't be.

The discussion is thus: it's probably a good idea, but it is NOT in tune with the spirit of democracy. Voters need not show any level of competence, nor should they have to. Studies have shown that crowds are smarter than you think, when they speak as one voice. While an informed constituency sounds great, remember that no constituency is ever *truly* informed -- hell, our congressmen and senators don't even read the bills they pass (or reject) anymore! There are millions who trust in common knowledge* and street wisdom; sometimes the view from the ground really does work.

The idealist's answer? Yes, we should have a very basic competence test - so basic that smart children as young as 10 or 12 should be able to vote. Answer like 5 questions including "who is the current President?" (And if you think that's too easy, you haven't seen Jay Leno's 'Jaywalking'.) Any more complicated than that and it's discrimination based on intellect. The competence test is testing ENGAGEMENT; as in, are you informed and interested enough to participate in democracy? If children vote, they're far far far far more likely to be engaged as adults, which will give you a more informed constituency in a few decades. Problem solved. ;)

The concept has merit in theory, but whom could we trust to design a "fair" test that would be the same for everyone? To even debate a proposed competency requirement, I think the test would need to be known in advance. In the unlikely event that it were approved, the test itself would need to be etched into a state's constitution so that no mere majority could tinker with it. Otherwise it would just be too prone to abuse (like the supposed "literacy" tests that barred blacks from voting in the South).

You can't do that.

I wouldn't be allowed to vote, let alone run for office.