OP is surely aware that Congress cannot raise the voting age. It would take another Constitutional amendment to overturn the XXVI.
In fact, all Congress can do is enforce it.
Twenty-Sixth 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.