Voting is a Constitutional right yet up until 1971 it was limited to 21 years and up.
It is no such thing. Under the original text of the Constitution, voting by the people was not mentioned at all. The Bill of Rights makes no mention of voting by the people, either. Voting by the people was (and largely still is) governed entirely by the States. Constitutional rules on voting began to appear piecemeal after the War Between the States. Your argument is silly: up until 1920, women could (and in many States, were) denied the power to vote. Are you willing to argue that women can, Constitutionally, be denied the right to keep and bear arms?
What part of "shall not be infringed" do you fail to comprehend?