What I've speculated is that perception of time is relative to how much you've experienced, i.e. how long you've been alive. When you're a child, a week seems

What I've speculated is that perception of time is relative to how much you've experienced, i.e. how long you've been alive. When you're a child, a week seems like a long time, because you haven't lived very many weeks. A year seems like an eternity, because relatively few have passed. As more of these increasingly large time units get behind you, years, then decades... you have a firsthand understanding of what living their respective durations feels like. It's like by living you're calibrating your ability to measure time properly, and then you die.