Time also equals missed opportunities. We are brought up with our perceptions in what it really means to "live" among our western culture. For example dating, marriage, family, traveling, education, dream jobs, lifestyles, and so on.
After we die, those opportunities we dreamed about are long gone hence the perception of how time flies. As long as the human race remains, perceptions, ideals and evolutionary theories will live ever after.
OK, maybe I'm babbling and ranting so don't quote me on that.... 
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I live as I choose or I will not live at all.
~Delores O’Riordan