This is a question posed to us from a reader, which I will begin to respond to here... at least until my assistant comes in and gets me back on my work-track.
I will interpret this question as a request for general public information rather than a request for legal advice. Legal advice requests and responses should be made in private communications between the client and the attorney - not in a public forum.
The 26th Amendment to the United States Constitution made it unlawful for the US government and the State governments to limit voting rights by age for those who are at least 18. One of the pressures to which the government was responding in 1971, when we passed this Amendment, was the Vietnam War. Many felt that if an 18 year old is old enough to be required to fight and die for his country, that he should also have the right to vote. It seems that this sentiment won the day.
Voting Rights Amendments have been consistently expanding our rights, as from the: 15th Amendments bar against racial discrimination in voting; the 19th Amendments granting of voting rights to women; and the 24th Amendment banning of poll taxes for federal elections. When our country was created, the only persons permitted to vote were white male property owners. And in some circumstances there were religious requirements for voting as well.
But it seems that land ownership is still sometimes used as a qualification for voting. In Montana, for example, there are types of voting rights that are based upon the number of acres of irrigable land that one might own (in 40 acre blocks).
Delaware School Referendum voting qualifications are set out at Title 14, Section 1077, which basically qualifies all residents of the district who are 18 or older.
Interestingly, the Delaware Constitution still has the 21 year old age requirement, but that would be ignored in light of the US 26th Amendment.
To accomplish a change in your local voting qualification laws, you should probably contact your State Senators, and Representatives, as your issue is primarly a State and local issue governed by State law... so long as it doesn't conflict with federal law. Perhaps support for such a change might be coordinated through forming or mobilizing political action groups for this purpose, as well.