There is a great difference between authorizing someone to drive a car and voting. It's not that either of those tasks is difficult, it's that they are extremely different. One requires hand-eye coordination, while the other requires an understanding of of our institutions, which goes far beyond knowing how to vote. It requires understanding the checks and balances the branches of government are supposed to exert on each other and the ones the states and people are supposed to apply to the federal government and vice versa. There isn't any similarity between the two responsibilities, apart from making judgments. In both cases, though, both require knowing certain facts to make wise judgements.