I don't have any figures to hand, but as ET says, it is the younger sections of the electorate that are least inclined to vote.
In most Western liberal democracies turnout has been dropping since the end of the second world war. Turnout for Presidential elections is around 50% in the USA, and in the UK for general elections it is 59%. After the war, turnout was about 80% in the UK.
I live in the UK, and there is a real concern here that young people aren't interested in politics - they don't trust politicians, and many believe their vote can't change anything. Of course, votes do change things, but equally there are millions of "wasted" votes each election.
It will probably come full circle one day, and turnout will rise, but for now it is falling.