Is advanced age and infirmity a good argument for clemency?

Arnold Schwarzenegger rejected that argument, made by lawyers on behalf of the murderer Clarence Ray Allen, who was just executed. It almost seems that there was an argument that keeping him alive would be a way of inflicting more punishment on him. At least, one might say that execution has lost the meaning it is supposed to have for the condemned man. But none of that states a reason for clemency.