This also assumes that you are wiling to live in retirement at the level that you sacrificed to live on to save for that retirement. If you live like a homeless person you can certainly retire very early and continue to live like a homeless person for quite a long time.

It also assumes that the averages will be the constant. Unfortunately, with the money that the Fed has been pumping into the system, we should be expecting run-away inflation soon. While having cash in the bank may seem like a good thing, when inflation makes that money virtually worthless having some hard assets like real estate, a business, precious metals, will be a much better place to be.