Final answer:
The Twenty-Sixth Amendment of the US Constitution, ratified in 1971, established the voting age nationally at eighteen years old, preventing the federal government and states from imposing a higher voting age.
Explanation:
The Twenty-Sixth Amendment to the United States Constitution, ratified in 1971, set the voting age at eighteen years old nationally. This amendment prohibits both the federal government and states from setting a voting age higher than 18, thus ensuring that US citizens aged 18 and older have the right to vote without age-based discrimination.
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