In most countries you can vote from 18 years of age. But this age has not been here for a long time, first country to adopt voting age of 18 was Czechoslovakia in 1946.
Initially the people from most countries had voting rights from the age of 21. Most recent developments are to decrease this age to 16. Supporters of this idea cite that today's youth have the necessary capacity to decide how to cast a vote. First leading democratic country to adopt voting age of 16 is Austria.
Iran is unique because it has increased minimum legal voting age from 15 to 18, two years ago.
Only country with a maximum voting age is the Vatican, where only cardinals younger than 80 can vote for a new Pope.
Some countries distinct between single and married people. For example, in Bolivia, single people can vote from 21 and married from 18. Citizens in Uzbekistan can vote from 25.