Psychology professor Laurence Steinberg wrote in the New York Times:
the skills necessary to make informed decisions are firmly in place by 16. By that age, adolescents can gather and process information, weigh pros and cons, reason logically with facts and take time before making a decision. Teenagers may sometimes make bad choices, but statistically speaking, they do not make them any more often than adults do.
For more, see his op-ed on “Why We Should Lower the Voting Age to 16”