Which amendment established the voting age as 18 years?

The 26th Amendment to the United States Constitution is significant because it lowered the voting age from 21 to 18 years. Ratified in 1971, this amendment was a response to the growing sentiment that those who were old enough to be drafted into military service should also have the right to vote in elections. The movement to lower the voting age gained momentum during the Vietnam War, highlighting the inconsistency of sending young men to fight while they were denied the opportunity to participate in the democratic process.

The other amendments mentioned serve different purposes: the 15th Amendment prohibits denying the right to vote based on race, the 19th Amendment grants women the right to vote, and the 23rd Amendment allows residents of Washington, D.C. to vote in presidential elections. Each amendment plays a critical role in expanding voting rights in the U.S., but it is the 26th Amendment that specifically addresses the voting age of 18 years.