Current revenue growth is around 50% annually; if that continues, it will reach the lower edge of your target (5X) in 48 months. Assuming of course it can maintain its margins.
Am I missing something or don't your assumptions assume that over those same 48 months Amazon's price remains static? Note that any assumption of Amazon's margins remain the same is kind of hard pressed. Their revenues this quarter was 40% greater then the same quarter last year - yet their earnings were down 73%.
The question was 'when will Amazon be making 5X what they make now?', and the answer (at current growth rates and current margins) is 48 months. Which is not a long time, thereby explaining the high P/E. If you think the growth will slow substantially or the margins will shrink substantially (or both) in the next 48 months, then the PE is too high. Otherwise, perhaps it's not so crazy after all.
