What factor could not be used to deny us citizens the right to vote according to the fifteenth amendment?

The Fifteenth Amendment prohibits denying the right to vote to U.S. citizens based on race, color, or previous condition of servitude. Therefore, factors such as race or color cannot be used to disenfranchise citizens. Other forms of discrimination, such as gender or age, are addressed by different amendments, making them irrelevant in the context of the Fifteenth Amendment.