Remember 1971?
AMENDMENT XXVI
Passed by Congress March 23, 1971. Ratified July 1, 1971.
Note: Amendment 14, section 2, of the Constitution was modified by section 1 of the 26th amendment.
Section 1.
The right of citizens of the United States, who are eighteen years of age or older, to vote shall not be denied or abridged by the United States or by any State on account of age.
Section 2.
The Congress shall have power to enforce this article by appropriate legislation.
You and I (among others here) can remember that as the result of the discrepancy between voting age and draft age. "If I'm old enough to die for my country, I should be old enough to vote for its leaders."
Who knows; maybe you're right. Maybe they should have raised the draft age to 21. A lot more lives would have been changed for the better, than were by lowering the voting age -- and it wouldn't have taken a Constitutional amendment.