A voting age is a minimum age established by law that a person must attain before they become eligible to vote in a public election. The most common voting age is 18 years; however, voting ages as low as 16 and as high as 25 currently exist (see list below). Most countries have set a minimum voting age, often set in their constitution. In a number of countries voting is compulsory for those eligible to vote, while in most it is optional.