I listed the life expectancy at 75 years old. If anyone wants to retire at 55, it mentions 20 years of retirement life. Excluding 2-3 million on housing (assume you already own), 2-3 million total personal expense equal to $8000 monthly allowance.
$8000 a month sounds ridicularly high, but consider
(1) $500 medical insurance premium (you do want to more than medicare standard)
(2) $1000-$2000 eat-out and social activities (don't forget donation).
(3) $1000 grocery and etc (your grandchildren want christmas gifts!)
(4) $500-1000 travel and vacation (you will not sleep on the floor anymore)
(5) $500 heat/electricity/gas
(6) $2000 tax, home insurace, etc.
That doesn't leave you much space. Some expenses are high, but imaging the inflation after N years (just think about how much $$$ federal print in past 3 years!)