Richer Winger had this story in Ballot-Access News:

Indiana is one of seven states that lets all voters age 65 and above vote by postal ballot (without excuse), but denies the same ability to younger voters. Some Indiana voters who are under age 65 have asked the U.S. Supreme Court to hear their case, on whether the 26th Amendment prohibits such disparate treatment. Tully v Okeson, 20-1244. The 26th Amendment says, “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.”

The Seventh Circuit had ruled that the 26th amendment does not apply to this situation. Here is the cert petition.