You could solve your problem by addressing the Tyranny of the Majority. There is no need to go and "Logan's run" the old.
The problem is not old people voting is that their vote has the power to ruin your life. The voter should have no more power over you then you have over your neighbor.
To be bound to the rule of 50%+1 is no better then being bound to the rule of 1. A dictatorship of the Masses is no less a dictatorship then the Dictatorship of a Despot.
"It is only by the abolition of the state, by the conquest of perfect liberty by the individual, by free agreement, association, and absolute free federation that we can reach Communism - the possession in common of our social inheritance, and the production in common of all riches." ~Peter Kropotkin
"Let us fight to free the world - to do away with national barriers - to do away with greed, with hate and intolerance. Let us fight for a world of reason, a world where science and progress will lead to all men’s happiness. Soldiers! in the name of democracy, let us all unite!" ~Charles Chaplin
"Communism is Anarchy. You can't regulate or reform your way to communism; it can only be achieved by direct action against state, class and capital."