Suffrage is the right to vote. Throughout most of history, the concept of suffrage, and especially being granted to all people, was quite foreign. This slowly became more of a reality in the United States and Europe over the last two centuries and in more recent times other parts of the world have followed suit.
While universal suffrage is becoming more common, there are age restrictions, obviously, associated with it. In the United States that age was 21 years of age for most of the country's history, but it was changed to 18 starting with the 1972 Presidential election.
Even in countries where universal suffrage is present, there can be self-imposed restrictions by certain groups that don't access that right. For instance, Jehovah's Witnesses choose not to vote for religious reasons.