The correct answer is: " The government mandated that all youth over 18 were granted the right to vote."
The Twenty-Sixth Amendment to the US Constitution was enacted in 1971 and it prohibits the states to set any requirements or limitations which prevent any US citizens who had already turned 18, from voting. The enactment was ratified at the state level, after the Congress' proposal, so that this ruling could become applicable to state and local elections too.