[apak]

I wonder if people have really thought through the maths of retiring at a young age on a fixed sum. You can't use the "headline figure" of 5% or whatever interest you think you can safely earn as your income: you have to subtract taxes, obviously, but also inflation if you expect to be doing this indefinitely. A cautious, but not ridiculously cautious estimate might be an income of 1.5% after taxes and inflation. Even that is probably hard to guarantee.
And even if you can manage that, you're allowing only for price inflation, not wage inflation, which means you risk ending up being stuck with a 2007 lifestyle in 2057.
(A worry, if extrapolating from 1957 is any guide.)

If I really had no plans for making further income and no easy option to fall back on if I needed, anything less than $2 million would leave me feeling seriously uneasy.