I don't think 16 year olds should really be driving cars, either. Most of them are irresponsible lunatics, in my experience. But they can learn to d'rive safely, and the earlier they start the faster they'll learn. Ideally they would be doing so in a simulator for the first few years. We should probably handle politics the same way - teach teenagers about the political process and help them get experience reasoning about political problems but without exposing others to the consequences of their errors until they're ready to fully participate.