Here are the arguments for and against:
Arguments: 16-years-olds are not old enough to vote; they're not responsible enough, smart enough, neurologically developed enough, and they'll probably vote Democrat.
Counter-Arguments: A 16-year-old can be just as rational as an adult, they may be just as smart, they have plenty of time to offset their lack of impulse control, and their political opinions ought to be irrelevant.